Programmer art
Programmer art refers to temporary graphics added by the game programmer to test functionality. When creating the graphics, speed is a priority and aesthetics are secondary (if they are given any consideration at all). In fact, programmer art might be intentionally bad. This draws attention to the fact that the graphics are merely placeholders and should not be shipped with the final product. This practice might also speed its replacement.
Common forms of programmer art include stick figure sprites, in platformers, and fuchsia textures, in games using 3d models. Games with a "top-down" perspective tend to use alphanumeric characters and simple 2-d shapes to represent characters and landscape elements.
Not all programmers decide to replace the art in their games prior to release, though. This is especially common in indie games, since indie developers generally lack the resources to commission large amounts of art for their games.