Terrain are the environmental surfaces can surroundings.
Examples of terrain include open floors, walls, trees, desks, streams, and so on. Terrain typically provides a backdrop and potential tactical challenges, but is not usually directly interacted with. Mining is one activity that is commonly does interact with Terrain.
Different kinds of terrain in roguelike maps can have a significant impact on how the player moves and fights.
Most terrain in roguelikes, be it the normal floor of a dungeon or cave to the grass of an outdoor map, allows for normal movement. However, adding other kinds of terrain will add a strategic element to combat and a challenge for a player that moves about on a map. Terrain can slow the player or block movement completely. It may require the player to dig through, swim or levitate to move through terrain.
Some terrain may contain both dangers such as traps or poisons and give positive effects to the player. Please refer to the compilation of terrain effects in roguelikes.