The small hand on a clock that points to the hours.
It goes once around the clock every 12 hours (half a day).
Example: in the clock on the left, the hour hand is just past the "8" so you know the time is just past "8 O'clock"
(And the large hand is the minute hand and it shows that it is 18 past the hour, so it is 18 past 8).
See: Minute Hand