An asylum seeker is a person who has sought protection as a refugee, but whose claim for refugee status has not yet been assessed. Many refugees have at some point been asylum seekers, that is, they have lodged an individual claim for protection and have had that claim assessed by a government or UNHCR. It is important to note that refugee status exists regardless of whether it has been formally recognised.
People do not "become" refugees at the point when their claims for protection are upheld – they were already refugees, and the assessment process has simply recognised their pre-existing status. People become refugees (and are entitled to international protection and assistance) from the moment they flee their country due to a well-founded fear of persecution, as stipulated in the Refugee Convention.
This means that a person can simultaneously be a refugee and an asylum seeker. Some refugees, however, do not formally seek protection as asylum seekers. During mass influx situations, people may be declared "prima facie" refugees without having undergone an individual assessment of their claims, as conducting individual interviews in these circumstances is generally impracticable (due to the large numbers involved) and unnecessary (as the reasons for flight are usually self-evident).
In other cases, refugees may be unable to access formal status determination processes or they may simply be unaware that they are entitled to claim protection as a refugee. While many refugees are, or have been, asylum seekers, not all asylum seekers are refugees. Some will be found to have valid claims for protection that entitle them to international protection and assistance. Others will be found not to be refugees, nor to be in need of any other form of international protection, and as such they are expected to return to their country of origin. (RCOA)