At the international level, no universally accepted definition for "migrant" exists. The term migrant was usually understood to cover all cases where the decision to migrate was taken freely by the individual concerned for reasons of "personal convenience" and without intervention of an external compelling factor; it therefore applied to persons, and family members, moving to another country or region to better their material or social conditions and improve the prospect for themselves or their family. The United Nations defines migrant as an individual who has resided in a foreign country for more than one year irrespective of the causes, voluntary or involuntary, and the means, regular or irregular, used to migrate. Under such a definition, those travelling for shorter periods as tourists and businesspersons would not be considered migrants. However, common usage includes certain kinds of shorter-term migrants, such as seasonal farm-workers who travel for short periods to work planting or harvesting farm products.
documented migrant: A migrant who entered a country lawfully and remains in the country in accordance with his or her admission criteria.
economic migrant: A person leaving his or her habitual place of residence to settle outside his or her country of origin in order to improve his or her quality of life. This term is often loosely used to distinguish from refugees fleeing persecution, and is also similarly used to refer to persons attempting to enter a country without legal permission and/or by using asylum procedures without bona fide cause. It may equally be applied to persons leaving their country of origin for the purpose of employment
irregular migrant: A person who, owing to unauthorized entry, breach of a condition of entry, or the expiry of his or her visa, lacks legal status in a transit or host country. The definition covers inter alia those persons who have entered a transit or host country lawfully but have stayed for a longer period than authorized or subsequently taken up unauthorized employment (also called clandestine/undocumented migrant or migrant in an irregular situation). The term "irregular" is preferable to "illegal" because the latter carries a criminal connotation and is seen as denying migrants' humanity.
skilled migrant: A migrant worker who, because of his or her skills or acquired professional experience, is usually granted preferential treatment regarding admission to a host country (and is therefore subject to fewer restrictions regarding length of stay, change of employment and family reunification).
temporary migrant worker: Skilled, semi-skilled or untrained workers who remain in the destination country for definite periods as determined in a work contract with an individual worker or a service contract concluded with an enterprise. Also called contract migrant workers.
IOM; Key Migration Terms; http://www.iom.int/cms/en/sites/iom/home/about-migration/key-migration-terms-1.html