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.
Uncheck the “save my password” box.
(travel) To remove a previously checked-in passenger from the check-in system, allowing changes to the ticket.