Unix time (also known as Epoch time, POSIX time, seconds since the Epoch, or UNIX Epoch time) is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, that is the time 00:00:00 UTC on 1 January 1970, minus leap seconds. It is a single signed number which increments every second, without requiring the calculations to determine year, month, day of month, hour and minute required for intelligibility to humans. Unix time is widely used in operating systems and file formats. The Unix time number is zero at the Unix epoch, and increases by exactly 86,400 per day since the epoch. This can be extended backwards from the epoch too, using negative numbers.