from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A second of time, as measured by an atomic clock, added to or omitted from official timekeeping systems annually to compensate for changes in the rotation of the earth.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A second of time added to the year occasionally to compensate for variation in the rate of Earth's rotation relative to the absolute standards of time.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a second (as measured by an atomic clock) added to or subtracted from Greenwich Mean Time in order to compensate for slowing in the Earth's rotation


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  • A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time, or UT1.

    The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. As of July 2015, all of them have been inserted either at the end of June 30 or December 31.

    This year a second was added on June 30, 2015; however, on January 21, 2015, several models of GPS receivers implemented the leap second as soon as the announcement was broadcast by GPS, instead of waiting until the implementation date of June 30.

    Because financial markets are vulnerable to both technical and legal leap second problems, the Intercontinental Exchange, parent body to 7 clearing houses and 11 stock exchanges including the New York Stock Exchange, is ceasing operations for 61 minutes at the time of the June 30, 2015 leap second

    July 15, 2015