It’s a very important distinction which affects every part of the process of entering the U.S and it’s critical for you to know if you expect to have an informed opinion on the matter. I’m only going to discuss the US process here as my illiteracy in most foreign languages makes researching their processes more difficult. We’ll start with immigrants, then asylum seekers and last refugees.
Global migration patterns have become increasingly complex in modern times, involving not just refugees, but also millions of economic migrants. But refugees and migrants, even if they often travel in the same way, are fundamentally different, and for that reason are treated very differently under modern international law. (unhcr.org) underlining added for emphasis
Immigrants/Migrants (referred to as Lawful Permanent Residents by USCIS/DHS)
According to the Immigration and Nationality Act, the definition of an immigrant is “any alien in the United States, except one legally admitted under specific nonimmigrant categories (INA section 101(a)(15))“. The non-legal definition of an immigrant is “a person who migrates to another country, usually for permanent residence.” (Dictionary.com)
For practical purposes, in this discussion, it would be someone who wants to come to America to study, to work, to live here permanently. Within this broad definition, there are also asylum-seekers and refugees. The difference is why they want to come to the U.S.
Economic migrants are choosing to leave their country of origin in order to seek out better economic conditions, etc.
According to the UN High Commission on Refugees, an asylum-seeker is someone who says he or she is a refugee, but whose claim has not yet been definitively evaluated. Bear in mind that the only world organization who has the authority to confer refugee status is UNHCR.
An asylum-seeker has left their country of origin in fear of their government or fleeing war and could also fit the following definition of a refugee but has not yet had refugee status conferred on them. Asylum-seekers may or may not be living in refugee camps (think Soviet defections on US soil we’ve all seen in movies), and may or may not be traveling with their families.
According to the 1951 Refugee Convention, a refugee is someone who “owing to a 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 to, or owing to such fear, is unwilling to avail himself of the protection of that country.” (unhcr.org)
In 2013, (unfortunately the latest year for which I can find compiled statistical data) the number of lawful permanent residents (aka immigrants/migrants) admitted to the US, was 990,553. In contrast, the number of refugees admitted to the US that same year was only 69,909.