Head slap is a gesture of frustration or disbelief, usually done by slapping one's own forehead with the palm of the hand. The two crossword solutions for this term are 'DOH' and 'OOPS'. 'DOH' is an interjection used to express surprise, realization, or disappointment, while 'OOPS' is an exclamation used to express surprise, regret, or apology. Both words are often used in response to a mistake or blunder.