Spoiler warning: Plot and/or ending details follow.
A refugee is an individual displaced from his or her home and forced to seek a new home elsewhere.
In the 2240s Starfleet resettled approximately 6,000 refugees from Epsilon Sorona II on Tarsus IV after a disaster on Epsilon Sorona required the removal of colonists from that world. Unfortunately many of these refugees would later wind up being murdered by former Governor Kodos and his people. (DSC novel: Drastic Measures)
A large number of Bajorans were displaced by the Cardassian Occupation of Bajor, and a number of Bajorans were forced to settle in refugee camps. Bajorans who lived in such camps included Ro Laren and Kira Nerys. (TNG episodes: "Ensign Ro", "Rascals";DS9 episode: "Emissary")
In the aftermath of the Borg Invasion of 2381, large populations of refugees were forced to seek shelter when and where they could. The large number of refugees on Pacifica precipitated a humanitarian crisis. (TNG novel: Losing the Peace)