For tagging purposes a whip is a tool with a long flexible line (lash) used to strike animals or people to aid in guidance or exert control through pain compliance or fear of pain. They are frequently depicted in bdsm.
A second style of whip are those that are a firm stick and lack a lash. For tagging purposes these images should be tagged riding crop instead.
The distinct loud sound of a whip "cracking" as it is swung is produced by a part of the lash breaking the sound barrier and generating a small sonic boom.