The summer ad winter Olympics take place every four years and are separated from each other by two years. The next winter Olympics will be held in 2014, as an example.
The Summer Olympics and the Winter Olympics are each held every four years, but not in the same year (actually 2 years apart). The Winter Olympics will next be held in 2014, while the Summer Olympics will be held again in 2016.
In the too much information area until 1992 the Summer and Winter games were held in the same year ... then starting in 1994 the Winter Olympics started the cycle of having Olympic games (summer or winter) every two years