Ever heard of a 61-second minute? Well, you're going to get one today. Time will stand still for one second today because a 'leap second' will be added to let a lagging Earth catch up to super-accurate clocks.
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time. The leap second will be inserted tonight at 23:59:60 UTC.