During the build up to WW2 many refugees left their homes in Germany, Austria and Czechoslovakia, usually due to their political views or religion - which they might have been imprisoned or killed for! However, many people, such as children were not able to emigrate, due to i.e. lack of money or transport, or simply the fact that it took time to acquire the travel documents to allow immigration. The Home Secretary at the time, Sir Samuel Hoare, decided to speed up the process by creating travel documents for groups rather than individuals.
Kindertransport is the collective term for all the organised ways refugee children left their country. After an appeal in Parliament and funding from groups such as charities (so that the children would not be a burthen on the public), the first Kindertransport departed on the 1st December 1938, and ran until 1939. The majority of children transported were Jewish, and homeless or orphaned children were prioritised as they had no-one to protect or support them.
The children were refugees, not asylum seekers, as the children were supposed to return to their families once the war was over, however many (mainly Jewish) remained in Britain for the rest of their lived instead, an example being if their parents were killed in concentration camps.