Dictionary

Unrestrained, not held back.

Not examined for accuracy, efficiency, etc.

Of a check box: not checked (ticked or enabled).

(crossword puzzles) Of a square: part of only one entry (that is, across or down, but not both).

To remove a checkmark.

Example: Uncheck the “save my password” box.

(travel) To remove a previously checked-in passenger from the check-in system, allowing changes to the ticket.