Real Dictionary

boat people
plural noun: Boat people are people who escape from their country in small boats to travel to another country in the hope that they will be able to live there.

boat people in American English
refugees from a certain country or region who try to immigrate to some other country, using small boats; specif., such refugees from Southeast Asia in the late 1970s
plural noun: refugees who have fled a country by boat, usually without sufficient provisions, navigational aids, or a set destination, esp. those who left Southeast Asia by sea as a result of the fall of South Vietnam in 1975

boat people in British English
plural noun: refugees, esp from Vietnam in the late 1970s, who leave by boat hoping to be picked up by ships of another country