Terrain is the type of material that a platform of a stage is composed of. Super Smash Bros. Melee, Super Smash Bros. Brawl, Super Smash Bros. 4, and Super Smash Bros. Ultimate are all known to use different types of terrain in their stages, and each game introduces new types of terrain for new uses.
Terrain can produce different footstep noises or visual effects when characters and other objects step or land on it. The main functional effect of terrain is traction; some types of terrain can increase or decrease traction, which means characters and objects will slide less or more, respectively, from movement on the terrain. There are also some types of terrain that are used to damage and launch players upon contact.
Terrain also affects the behaviour of some special moves. In Melee, Yoshi's ability to accelerate during Egg Roll is affected by terrain. In Brawl, Olimar's Pikmin Pluck has its speed and the type frequency of resulting Pikmin affected by the terrain he is standing on.
None of the different types of terrain have an effect on gameplay outside of cosmetics, with the exception of ice and other slippery surfaces.
The colours in this table are taken from Melee's debug mode.
Smash 4 terrains
Smash 4 has 33 different terrain types. Most of them only differ cosmetically, but a few have different traction, which is listed as a multiplier in the table below. Several of the terrain types are unknown and may be dummied leftovers from Brawl, while others are known but have unknown usage and may be unused.
Ultimate has 44 different terrain types as of the latest version; the base game had 43 types. Most of them only differ cosmetically, but a few have different traction, which is listed as a multiplier in the table below. It appears that most terrain types in Smash 4 carry over to Ultimate, but notably, Grass no longer has increased traction.