It is easy to see how electrons can move around the lattice and carry a current. However it is not quite so obvious for holes. This happens when an electron from a complete orbit moves to fill a hole, leaving a hole where it came from. Another electron from another orbit can then move in to fill the new hole and so forth. The movement of the holes in one direction corresponds to a movement of electrons in the other, hence an electric current.
From this it can be seen that either electrons or holes can carry charge or an electric current. As a result, they are known as charge carriers, holes being the charge carriers for a P-type semiconductor and electrons for an N-type semiconductor.