Since the world is approximately a sphere, and the sun is only on one side of it, in some places it's light and in some places it's dark. So people decided that every so often they'd redefine when the time is, so that "noon" is during daylight hours, and "midnight" is sometime in the dead of night. Kinda.

Since seasons also change when it's light/dark most places change what the time is twice a year calling it daylight savings. And, during the second world war, England, which was being bombed at night went onto daylight savings several times but never came off it inbetween times, so that people were going to bed very early so they didn't tend to have lights on at night that bombers could use to locate cities. This can be seen by the following command
zdump -v /usr/share/zoneinfo/Europe/London | grep 1945

See the TimeNotes page for information on TimeZones as applied to your OperatingSystem.