Can't wait another second for 2009 to get here? Well, you'll have to. Yes, add an extra 1 to your countdown this year. The International Earth Rotation and Reference Systems Service is adding an extra second to the year due to the Earth's revolution around the Sun not being exactly a year. It's the organization that monitors the difference in the two timescales and calls for leap seconds to be inserted or removed when necessary.
Basically it's like a leap second.
Full article here:
This year will be just a second longer
'Leap second' is tacked on to clocks every so often to keep them correct