From the lecture of Alexander Kuna: Where did the leap second come from?

The presentation was introduced in the spirit of Werich's definition of time: "people came up with time in order to know - from when to when and what do you want for it" at the Pilsen Observatory and Planetarium on January 8th, 2014. He talked about the history of time keeping and the definition of basic unit - the second. For those who do not know where the name comes from,  the second was the designation for the second (seconde) sexagesimal division of hours already at the time of Ptolemy. The Czech, often misused, second comes from a similar expression in Russian (второй = second). Other standards (ie standards of individual physical quantities) are defined with the use of time constants because time can be so easily and accurately measured. For example, a meter is the distance traveled by light in vacuum during a specific fraction of time. The definition of a meter is therefore based on two constants - the speed of light and a time interval.

The leap second  is inserted at most twice a year in a way that the last minute of the day has 61 seconds. 

For more information, read the full article on the website of the   Observatory and Planetarium in Pilsen here. (in Czech only)