The hour (common symbol: h or hr, h being the international form of the symbol) is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds. It is approximately 1⁄24 of a mean solar day.
An hour in the Universal Coordinated Time (UTC) time standard can include a negative or positive leap second, and may therefore have a duration of 3,599 or 3,601 seconds for adjustment purposes.
Although it is not a standard defined by the International System of Units, the hour is a unit accepted for use with SI, represented by the symbol h.
The Middle English word ure first appears in the 13th century, as a loanword from Old French ure, ore, from Latin hōra.Hora, in turn, derives from Greek ὥρα ("season, time of day, hour"). In terms of the Proto-Indo-European language, ὥρα is a cognate of English year and is derived from the Proto-Indo-European word *i̯ēro- ("year, summer").
The ure of Middle English and the Anglo-French houre gradually supplanted the Old English nouns tīd (which survives in Modern English as tide) and stund. Stund is the progenitor of stound, which remains an archaic synonym for hour. Stund is related to the Old High German stunta (whence German Stunde, "hour, lesson"), from Germanic *stundō ("time, interval, while").