From the Glossary of The Wheel of Time

There are threads to the One Power, and each person who can channel the One Power can usually grasp some threads better than others. These threads are named according to the sorts of things that can be done under them - Earth, Air, Fire, Water, Spirit - and are called the Five Powers. Any wielder of the One Power will have a greater degree of of strength with one, or possibly two, of these, and a lesser stregth in the others. Some few may have great strength with three, but since the Age of Legends no-one has had great strength with all five. Even then this was extremely rare. The degree of strength can vary greatly between individuals, so that some who can channel are much stronger than others.

Performing certain acts with the One Power requires ability in one or more of the Five Powers. For example, starting and controlling a fire requires Fire, and affecting the weather requires Air and Water, while Healing requires Water and Spirit.

While Spirit was found equally among men and women, great ability with Earth and/or Fire was found much more often among men, with Water and/or Air among women. There were exceptions, but it was so often that Earth and Fire came to be regarded as male powers and Water and Air as female. Generally, no ability is considered stronger than any other, though there is a saying among Aes Sedai: "There is no rock so strong water and wind cannot wear it away, no fire so fierce that water cannot quench it or wind snuff it out." It should be noted that this saying came into use long after the last male Aes Sedai was dead. Any equivalent saying among male Aes Sedai is long lost.