A sprite is a small block of patterns that can be positioned anywhere on-screen. Many games use sprites to draw the foreground objects, such as the player character, the HUD, enemies and so on.
Take the screenshot for example. The HUD, spilled rings, spikes and the spring are all sprites, as well as Sonic himself. Note the rings are appearing above the spikes, as their priority is higher and they are in the link list later. The HUD can be seen above everything else, as it has it's priority bits set and is last in the link table.