There are four common strokes associated with swimming: butterfly, backstroke, breaststroke, and crawl stroke. Breaststroke and backstroke are considered ‘rest’ strokes; crawl stroke, also known as freestyle, and butterfly are known as ‘power’ strokes. A rest stroke uses less energy to travel the same distance, however; it takes longer to achieve this distance. A power stroke uses more energy and covers greater distances in less time.
The sidestroke and elementary-backstroke are two more rest strokes used in swimming. Each of these are not used competitively, but instead are taught to beginners to help them understand all aspects of swimming.
Each stroke is unique in body position and the method used to propel each body
differs for every stroke.
(http://www.ccatswimming.com/pictures/index.html)