Second by which a month is extended at the end of quarter in UTC reference time. This offsets the effect of the slower rotation of the earth with respect to TAI (Temps Atomique International). A leap second day has 86401 seconds and the leap second is represented by 23:59:60. The standard POSIX.1:2001 does not support leap seconds and each day has 86400 seconds. In times based on the POSIX standard, any leap seconds are rounded to valid times.