Gammon terrine is a classic dish made with cured and cooked gammon, which is a type of ham. The gammon is cooked until tender and then pressed into a terrine mold to set. It is typically served cold and sliced thinly. The terrine can be flavored with herbs, spices, or other ingredients like mustard or pickles. It is a versatile dish that can be enjoyed as an appetizer, a main course, or in sandwiches.