As quoted from wikipedia,

"Egg tarts, custard tarts, or egg custard tarts are a kind of pastry popular in many parts of the world, particularly in Chinese and Western European cuisines. The tarts consist of an outer pastry crust that is filled with egg custard and baked."

Note: Traditional Egg Tarts are not to be confused with "Portuguese Egg Tarts" which have a creme brulee and caramel like top and is sweeter in comparison.Read the full article