not just unit graphics...sprites (in game terms) are the images for the objects in 2d games. in 3d games, you have textures and objects, no sprites.
examples:
a marine is based off of some 100+images. each of those images is a sprite.
each tile type in a tile set is made up of multiple sprites. each one of those sprites is a little square that when put together makes the tile. ever notice how tiles seem to varry a lot?
a doodad is a sprite. like the tiles, it is made up of squares, but they are always plaec in the same way EXCEPT for ones that have to show multiple terain types in the background of it.
examples from other games:
Wolfenstein 3d (even though its 3d, it is still made of 2d objects): the walls are sprites, the gun is a sprite, blood on floor, bodies on floor, ect.
AND YOU CAN MAKE TRIGGERS WITH STARFORGE. you just need to type a whole lot....