A doorstop (or door stop or doorstopper) is a tool.
There are two types. One holds a door open (or stops it from closing), and the other stops the door from hitting a wall.
Doorstops that keep the door from hitting a wall can be put on the door, or on the wall, or on the floor in front of the wall.
Doorstops that are used to keep a door open come in two varieties: