As the global debate surrounding migration issues grows, BBC News Online looks at some of the terms that appear most frequently in the discussion.
Scroll down the page, arranged alphabetically, or use the links below to go direct to the explanation. Within each explanation, definitions for terms in bold can be found elsewhere on the page.
Described by the UN as someone who has made a claim that he or she is a refugee and is awaiting the determination of his or her status.
The term contains no presumption either way - it simply describes the fact that someone has lodged the claim. Some asylum seekers will be judged to be refugees and others will not.
The emigration of a large number of a country's highly skilled and educated population to countries where they can expect to find better economic and social opportunities.
Someone who leaves behind their country of origin in order to improve their quality of life. The term is often used to refer to those attempting to enter a country without legal permission and/or those who asylum procedures without bona fide cause.
The International Organisation for Migration defines this as the non-voluntary movement of someone who wishes to escape an armed conflict, violence, the violation of their rights or a natural or man-made disaster.
The term applies to refugee movements as well as to those caused by human trafficking and the forced exchanges of populations among states.
A Green Card allows an immigrant to live permanently in the US.
There are several types of Green Card and are mostly given to people sponsored by their companies, people who are related to someone in the US, or those seeking asylum.
The United States' H-1B programme allows an employer to temporarily employ a foreign worker in the US on a non-immigrant basis in a specialty.
The UN defines human trafficking as: "The recruitment, transportation, transfer, harbouring or receipt of persons, by means of the threat or use of force or other forms of coercion, of abduction, of fraud, of deception, of the abuse of power or of a position of vulnerability or of the giving or receiving of payments or benefits to achieve the consent of a person having control over another person, for the purpose of exploitation."
This exploitation can take different forms, including:
- prostitution or other kinds of sexual exploitation
- forced labour or services
- slavery or practices similar to slavery
- the removal of organs.
Victims of trafficking have either never consented to the trafficking or their initial consent has been rendered meaningless by the coercive, deceptive or abusive actions of the traffickers.
An all-encompassing term usually taken to mean someone who leaves their native land and goes to another country as a permanent resident (as distinct from a holidaymaker, for example).
The International Organisation for Migration describes an irregular migrant as someone who, owing to illegal entry or the expiry of their visa, lacks legal status in a transit or host country.
The term applies to migrants who infringe a country's admission rules, seek asylum without due cause and any other person not authorised to remain in the host country.
Melting pot model
The term refers to the idea that immigrants and other minority groups are "absorbed" into an integrated mainstream society. Such a "melting pot" is expected to result in a relatively homogenous society, with a strong sense of national identity.
The term was taken from the title of a 1908 play by London-born Israel Zangwill and has traditionally been applied to the United States and the process of Americanisation. However, in recent years many commentators have questioned the validity of the melting pot model, dismissing it as assimilationist and racist.
Usually described as someone who enters a country other than that of which they are a citizen for at least 12 months, after having been absent for one year or longer.
A foreigner who is admitted by a state for the specific purpose of exercising an economic activity which is remunerated from within the receiving country.
The length of stay and type of employment are usually restricted.
Also known as the multicultural model, the mosaic formula is based on the belief that people of different backgrounds can fit together without losing their original identity.
One of the main proponents of this model is Canada. Its 1985 Multiculturalism Act says immigrants and their descendents should be free to keep and promote their cultural heritage while fully participating in Canadian society.
Migration is often analysed in terms of the "push-pull model", which looks at the (negative) push factors which drive people to leave their countries and the (positive) pull factors which attract them to their new countries.
The 1951 Convention on Refugees describes a refugee as: "A person who is outside his/ her country of nationality or habitual residence; has a well-founded fear of persecution because of his/ her race, religion, nationality, membership in a particular social group or political opinion; and is unable or unwilling to avail himself/ herself of the protection of that country, or to return there, for fear of persecution."
Monies earned or acquired by migrants that are sent back to their country of origin.
The population that is necessary to offset declines in the general population, the population of working age, as well as to make up for the ageing of a population.
Refers to the movement of people who return to their countries of origin or habitual place of residence after spending at least one year in another country.
Return migration can be voluntary or the result of an expulsion order.
Smuggling of migrants
The UN defines the smuggling of migrants as: "The procurement in order to obtain, directly or indirectly, a financial or other material benefit, of the illegal entry of a person into a state of which the person is not a national or permanent resident."
It differs from human trafficking in that in involves the consent of the migrants involved and ends with the arrival of the migrants at their destination.
1951 Convention Relating to the Status of Refugees
A key international legal document, now with 145 signatories, that defines who is a refugee, their rights and the legal obligations of states. Drawn up by a special UN conference, a significant provision stipulates that refugees should not be returned to a country where he or she fears persecution.