A standard (or rotary drill/driver) moves the drill bit in a clockwise motion enabling the drill bit to bore into the material being drilled.

A hammer drill has this function but also has a "hammer" feature that moves the drill bit in a forward motion as well.

This function makes drilling into masonry a great deal easier, as masonry presents a lot of resistance to the standard rotary drilling method, meaning it will take longer to drill the area required.