A clock is a piece of equipment used to track the passage of time.
When the USS Archon visited Beta III, the computer Landru scanned the computer systems of the Archon, and incorporated much of what it found on human culture into its program. As a result, clocks with Arabic numerals soon began appearing in the Betan community, with the clocks sped up to account for the 22 hour rotational period of Beta III. (TOS novel: Ex Machina)
In 2376 a clock killed the Bajoran Woros Keyth when it hit him after the artificial gravity shifted in his office on Deep Space 9 during a Jem'Hadar attack. The impact caused injuries leading to fatal brain damage. (DS9 novel: Avatar, Book One)