What is the difference between 2 wheel drive and 4 wheel drive?

2wd is when one set of axles(or drive wheels),either front or rear propells the vehicle 4wd is when all drive wheels (axles) supply the motivation. In reality unless the vehicle is equipped with LSD, Posi-trac, True-trac, Detroit-locker or one of the many other names that limited-slip or locking differentials go by, the preceding statement is only half correct.