The fixed block of time during which an employee is expected to be at work; excludes flexitime and leave.

(figuratively) The hour at which any major event planned for the future is set to begin, as used in United States military.

The very early morning, just after midnight, when most people are asleep.

(idiomatic) The times of the day when traffic jams are commonplace, due mainly to people commuting to or from work.

The hand of a clock or watch face that revolves twice each day and indicates the hours.

(physics) a unit of electric charge, equal to the charge transferred by a current of one ampere in one hour through a specified point in a circuit, equal to 3600 coulombs.

(idiomatic) The time at (or very close to) the start of the next hour of time.

Happening hourly, but at 30 minutes past each hour; ie, 08:30, 09:30 etc. / Happening on the hour and at 30 minutes after the hour. / (soccer) At thirty minutes into a half.

(US) A period when traffic is light / time outside normal business hours

The very early morning; the early morning hours; the nighttime hours following midnight, when most people are asleep.