Daylight saving is basically that. During the summer, the time is taken back an hour to use the extra time of daylight to avoid illumination costs which are pretty high. During the winter, it's advanced an hour to save the daylight time which is less than in the summer, again, to avoid illumination costs. Some countries don't respect it for various reasons. Argentina, for example, because it was a mess and no one organized themselves making a stuffload of problems. IIRC, some parts of Japan also don't follow it.
