Level

In rougelikes there are two uses of the term level.

Dungeon Levels

A dungeon level is like a level in a building. However, they are below ground (!). In roguelikes they can be either persistant or non-persistant. Persistant levels are when the game remembers a previous level you went on and the state you left it in. sometimes games have semi-persistant levels where the layout is remembered but the monsters and items get randomised. non-persistant levels get generated again once it is requested again.

Experience Levels

These are levels of skill usually related to strength of your character. If you kill so many monsters you may ascend to the next level. this will become increasingly difficult if an experience curve is in place.