Everyone knows about the Leap Year, but the 'Leap Second' is rather more obscure.
But international experts about to meet in Switzerland are pondering whether to get rid of it in a move that has provoked quite a row.
The world's measure of time, known as Coordinated Universal Time or UTC, is managed in Paris.
Measurements from hundreds of atomic clocks around the world are sent there to keep the best average measure.
The problem is the Earth's orbit around our Sun isn't perfect, nor is speed of the Earth's rotation.
Each day isn't exactly 24 hours long which is the reason why leap seconds have been added since 1970.
The last time a leap second was added was on New Year 2008 -- but at the world time meeting in Geneva -- at least 16 nations will call for them to be scrapped.
