Daylight saving time
Daylight saving time (also called DST, or Summer Time) is the local time a country adopts for a portion of the year, usually an hour forward from its standard official time.
It is a system intended to "save" daylight (as opposed to wasting it by, say, sleeping while the sun shines). The official time is adjusted forward during the spring and summer months, so that the active hours of work and school will better match the hours of daylight.
Locations that observe or do not observe DST are listed in the article Time zone#List of time zones and contained areas.