Daylight saving time (also called DST, or summer time) is a system intended to "save" daylight. The official time is adjusted forward, (usually) one hour from its official standard time, remaining that way for the duration of the spring and summer months. This is intended to provide a better match between the hours of daylight and the active hours of work and school. DST is most commonly used in temperate regions, due to the considerable variation in the amount of daylight versus darkness through the seasons in those regions.
One of the major reasons given for observing DST is energy conservation. Theoretically, the amount of residential electricity needed in the evening hours is dependent both on when the sun sets and when people go to bed. Because people tend to observe the same bedtime year-round, by artificially moving sunset one hour later, the amount of energy used is theoretically reduced.