Well, this is in fact anything that is gelified with layers of ingredients or multiples ingredients. Some recipes have a name of their own. But anything that uses the same techniques to have a gelified block you can cut in slices works.
The idea is that it's easier to serve some ingredients in a terrine as you can easily slice them. Nice for traiteurs (people selling cooked food)
A terrine last a little longer than other dishes.
Beef gelly can bring some flavors to the front.
You can have a very nice combination of colors
It's fairly easy to prepare