Sharp, shrill sound

The crossword question “Sharp, shrill sound is YAP” refers to the definition of the word YAP. YAP is a verb that means to bark sharply or shrilly like a small dog. The definition relates to the sound that the animal makes and is often used in a negative connotation to describe a dog that barks incessantly or annoyingly. In crossword puzzles, it is common to have clue-answer pairs that refer to specific definitions of words, and in this case, the answer to the crossword question is simply YAP.