Many countries, and sometimes just certain regions of countries, adopt daylight saving time (DST), also known as summertime, during part of the year. This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn (“spring forward,” “fall back”).
Modern DST was first proposed in 1907 and was in widespread use in 1916 as a wartime measure aimed at conserving coal. Despite the controversy, many countries have used it off and on since then; details vary by location and change occasionally. Countries around the equator usually do not observe daylight saving time since the seasonal difference in sunlight is minimal.