Yes, you read it right just like a leap year we had leap second on June 30th, 2015. June 30th ended day with GMT 23:59:60 odd time adding a second to earth’s atomic time. NASA stated this has been done to cope up with the earth’s rotating speed as its gradually slowing down.
And to your surprise this was not the first time that leap second was added to the world time. In fact it was started back in 1972 & this year was the 26th time that we have adjusted our time with earth’s rotation which is managed by International Earth Rotation and Reference Systems Service (IERS) which keeps track of time for the world. The last leap second was added on June 30, 2012. And it had many websites like Reddit, FourSquare, Gawker, StumbleUpon, LinkedIn, Yelp to collapse. It also had contributed for delay or cancelled flights. Google has been added up a fraction of second from past few years so they don’t face sudden shift of time.
By the year 2100 there would be a time difference of 2 to 3 minutes between earth’s actual rotations to our atomic time if we don’t add a leap second. So to keep our atomic clock synchronizes with the sun this practice has to follow. IERS informs 6 months prior to the time of shift. There is not periodic time regulation shift like leap year it has to be performed whenever the time difference 0.09 sec.
Since January 1972, timekeeping has, been maintained time in accordance with the atomic time scale. The Earth is currently losing about three-thousandths of a second per day, and, atomic clocks are just over six-tenths of a second fast on UTC right now. The addition of the leap second will keep the difference from exceeding nine-tenths of a second.
Leap seconds are inserted, when needed, either on June 30 or at the very end of the year, on Dec. 31.