Steps are blocks, found in Survival when destroying Coal or crafted in Indev, Infdev, or Alpha using three cobblestone. Step blocks were formerly called stair blocks until a new stair block was added. Steps form a half block and can be walked up by the player without the need to jump. Placing two steps on top of one another makes it a full block and breaking it will only yield one step instead of the two used to place it.
Trivia
Single-steps will destroy gravel and sand blocks that fall onto them.