Migration terms and definitions
Migration is part of the wider concept of 'movement,' which ranges from commuting to permanent emigration.
An immigrant is defined as someone who intends to stay in the UK for a year or more having lived outside it for a year (so measures of immigrants could include Britons returning home from living abroad).
An emigrant is someone who intends to leave the UK for a year or more having been inside the UK for a year or more.
A refugee is someone who has left their home because of a well-founded fear of being persecuted in that country for various reasons. The official international definition is someone who, "owing to well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion, is outside the country of his nationality and is unable, or owing to such fear, is unwilling to avail himself of the protection of that country; or who, not having a nationality and being outside the country of his former habitual residence as a result of such events, is unable or, owing to such fear, is unwilling to return to it" (United Nations Refugee Convention, 1951 and 1967 Protocol).
An asylum seeker is a person who is trying to claim refugee status, usually on political or religious grounds.