International Date Line
There are many groups of islands in the Pacific Ocean. These groups belong to states which do not want some islands on one side of the date line, and the rest on the other. They have therefore decided to move the date line, so that all islands are in the same time zone. Examples of this are the Aleutian Islands, which are on both sides of the 180° meridian. They are part of Alaska, and are therefore all in the UTC-10 timezone. The date line has a bump to the west, there.