The obvious answer is sanded grout has sand. But the in depth
answer has many differences.
Sanded grout which is the most common, can be used in a grout
joint from 1/8" to 1/2" (and larger but check the grout). Sanded
grout scratches many tile like glass.
Non sanded grout can only be used on joints 1/8" or less. Non
sanded grout is typically seen on marble and granite tile, many
wall tile, and all glass tile.