What is Migration? Definitions, Types, and Key Concepts

Every year, millions of people in India pack their belongings and head somewhere new. A farmer’s son boards a train to Mumbai to work on a construction site. A bride moves to her husband’s village after marriage. A software engineer accepts a job offer in Bengaluru. A family flees floods in Assam and rebuilds life elsewhere. Each of these journeys, big or small, falls under one umbrella term in population studies: migration. Understanding what migration actually means, how it is classified, and how official agencies measure it is the foundation for studying one of the most powerful forces shaping societies today.

What is migration? 🔗

In the simplest sense, migration is the movement of people from one geographical location to another. But population scientists need a more precise definition than that. Not every movement counts as migration. A weekend trip to your hometown, a pilgrimage, or a holiday in Goa is not migration. What makes a movement “migration” is a change in the usual place of residence for a meaningful duration.

The International Organization for Migration (IOM) describes migration as the movement of people away from their usual place of residence to a new place of residence, either across an international border or within a State. The IOM also notes that there is no single universally agreed definition, which is why different agencies set their own criteria for time and distance.

Three elements are central to any working definition of migration:

Change of residence: The person must shift their usual place of stay, not just travel temporarily.
Crossing a boundary: The movement involves crossing some administrative or political boundary, such as a village, district, state, or international border.
Duration: The stay at the new place must last for a defined minimum period, which varies by agency.

Why definitions matter in population studies 🔗

Migration data drives policy on housing, jobs, public health, education, and welfare. If the definition is too narrow, short-term workers and seasonal migrants are missed. If it is too broad, the data becomes noisy and less useful. This is why the Census of India, the National Sample Survey Office (NSSO), and the IOM each apply their own carefully worded criteria. The differences in their definitions explain why migration numbers in India can range from around 309 million to 450 million depending on which source you read.

Types of migration 🔗

Migration is classified in several overlapping ways. The most common classifications are based on the boundaries crossed, the duration of stay, the motivation behind movement, and the degree of choice involved.

Internal versus international migration 🔗

The first and broadest classification is based on whether the movement happens within a country or across national borders. Internal migration is the movement of people within a country, while external or international migration involves crossing national boundaries. Internal migration dominates the Indian story. According to the 2011 Census, internal migrants in India numbered around 450 million, a 45 percent increase over 2001, while international migrants made up only about one percent of total migration.

Internal migration in India is further divided based on administrative boundaries:

Intra-district migration: Movement within the same district. This is the largest category, accounting for roughly 62 percent of all internal moves.
Inter-district migration: Movement between districts within the same state, contributing another 26 percent.
Inter-state migration: Movement across state borders, which makes up only about 12 percent of internal movement.

International migration, by contrast, involves crossing country borders. It includes emigration (people leaving India to live abroad) and immigration (people from other countries settling in India). India is the world’s largest source of international migrants, with a significant diaspora in the Gulf countries, North America, the UK, and Southeast Asia.

Rural-urban streams 🔗

Within internal migration, demographers track four directional streams based on origin and destination: rural-to-rural, rural-to-urban, urban-to-rural, and urban-to-urban. Rural-to-rural migration is historically the largest stream in India, driven largely by marriage. However, rural-to-urban migration is a major driver of urbanisation, fuelling the rapid growth of cities like Mumbai, Delhi, Bengaluru, and Kolkata.

Temporary versus permanent migration 🔗

Duration is another key dimension. Permanent migration involves a long-term or lifelong relocation, such as a family settling in a new city for generations. Temporary migration includes short-term, seasonal, and circular movement, where the migrant returns home after some time. A sugarcane cutter who travels to western Maharashtra for the harvest season and returns to her village every year is a classic temporary migrant. Short-term migration is especially common in India’s informal labour sector but is often underreported in official data.

Voluntary versus forced migration 🔗

Migration can also be classified by the degree of choice involved. Voluntary migration happens when a person freely decides to move, usually for better opportunities, education, or marriage. Forced migration, on the other hand, is driven by circumstances beyond the individual’s control, such as war, persecution, communal conflict, development projects, or natural disasters. The displacement of people due to dam construction, the 1947 Partition, or the more recent floods in Uttarakhand and Kerala are examples of forced migration.

Motivation-based categories 🔗

Looking at why people move gives us another useful classification:

Economic migration: Driven by employment, business, or better wages. This is the dominant reason for male migration in India.
Social migration: Driven by marriage or family reasons. Marriage is the leading cause of female migration; marriage accounted for over 71 percent of all migration in the 2020-21 NSSO data, including 86.8 percent of female migration.
Political migration: Driven by conflict, refugee crises, or political instability.
Environmental migration: Triggered by climate change, droughts, floods, or other ecological pressures.

How official agencies define a migrant 🔗

Three agencies stand out when it comes to defining and measuring migration in the Indian and global context: the IOM, the Census of India, and the NSSO. Each has its own working definition, and the differences are not just technical, they shape what gets counted and what does not.

The IOM definition 🔗

The IOM defines a migrant as any person who is moving or has moved across an international border or within a State away from their habitual place of residence, regardless of the person’s legal status, whether the movement is voluntary or involuntary, what the causes for the movement are, or what the length of stay is. This is a deliberately wide umbrella term, designed to cover refugees, workers, students, marriage migrants, and displaced people alike. For demographic data, the United Nations also uses a stricter sub-definition: a long-term migrant is someone who lives outside their country of origin for at least 12 months.

The Census of India definition 🔗

The Census of India has tracked migration since its very first edition in 1881. It uses two criteria to identify a migrant:

Migration by place of birth (POB): A person is counted as a migrant if their place of enumeration is different from their place of birth.
Migration by place of last residence (POLR): A person is counted as a migrant if their current place of residence is different from where they previously lived for six months or more.

The Census also collects information on the duration of residence at the place of enumeration and the reasons for migration. This dual approach captures lifetime migration as well as more recent moves, but it tends to miss a significant number of short-term migrants who circulate between origin and destination.

The NSSO definition 🔗

The NSSO, now operating under the Ministry of Statistics and Programme Implementation, complements the Census with sample-based surveys. Its definition is built around the concept of Usual Place of Residence (UPR). According to the NSS 64th round on Migration in India, a household member whose last usual place of residence was different from the present place of enumeration is considered a migrant. The UPR is defined as a place where a person has stayed continuously for six months or more.

Crucially, the NSSO also tries to capture short-term migration. In its earlier rounds, short-term migrants were those who had stayed away from their village or town for between one and six months during the last year for employment. The upcoming National Migration Survey planned for 2026-27 is set to widen this further, with short-term migration now covering stays of 15 days to six months, making it more sensitive to circular labour movement. As per the most recent Migration in India 2020-21 report based on PLFS data, the overall migration rate stood at 28.9 percent, with 47.9 percent among females and 10.7 percent among males.

Putting it all together 🔗

Migration, at its core, is about people changing where they live. But that simple idea expands into a rich web of categories: internal and international, temporary and permanent, voluntary and forced, economic and social. The IOM offers the broadest umbrella definition; the Census of India uses place of birth and place of last residence as anchors; and the NSSO relies on the idea of usual place of residence with a six-month threshold. Each definition serves a purpose, and together they help us understand the scale, direction, and motivation behind one of the most defining demographic processes of our time.

For students of population studies, the key is to recognise that the “meaning” of migration is not fixed. It shifts with the lens you use, whether that lens is economic, social, geographic, or administrative. And in a country where nearly one in three people is a migrant, getting these definitions right is far from an academic exercise. It directly shapes policies on labour rights, public services, urban planning, and welfare portability.

What do you think? If short-term and circular migrants are routinely undercounted by both the Census and NSSO, how might this affect welfare schemes designed for vulnerable workers? And in your own family or neighbourhood, can you identify someone who fits the IOM definition of a migrant but might not show up in official Indian statistics?

References

1. https://www.iom.int/fundamentals-migration
2. https://blogs.worldbank.org/en/peoplemove/internal-migration-india-grows-inter-state-movements-remain-low
3. https://www.migrationpolicy.org/article/internal-labor-migration-india-raises-integration-challenges-migrants
4. https://factly.in/data-nsso-data-indicates-high-migration-to-union-territories-from-other-states/
5. https://weblog.iom.int/who-migrant
6. https://documents1.worldbank.org/curated/en/429181519662555108/pdf/WPS8356.pdf
7. https://www.mospi.gov.in/sites/default/files/publication_reports/533_final.pdf
8. https://www.drishtiias.com/daily-updates/daily-news-analysis/national-migration-survey-2026-27
9. https://visionias.in/current-affairs/news-today/2026-02-03/society/national-statistics-office-nso-to-conduct-survey-on-migration-across-india