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

The experience levels define how experienced a character is on surviving inside the game world; they are usually related to the strength and overall performance of the character. If you obtain a number of experience points, via monster killing or another means determined by the game, you may ascend to the next level. This leveling up becomes increasingly difficult according to the experience curve of the game.