Here is the US (HISA) definition of abuse. I agree with that.
Definition of Abuse in Whip Use (HISA Rule Series 2000)
Abuse includes, but is not limited to:
Exceeding the Strike Limit:
Jockeys are limited to six strikes per race.
More than six strikes may trigger penalties, especially if deemed excessive or unnecessary.
Striking the Horse in Prohibited Areas:
Whip use is restricted to the shoulder or hindquarters.
Striking the horse on the head, neck, or belly is considered abusive.
Using the Whip with Excessive Force:
Whips must be used in a controlled, non-aggressive manner.
Excessive force or repeated striking that causes visible injury or distress is classified as abuse.
Using the Whip After the Horse Has Clearly Won:
Continued use of the whip after the outcome is obvious is considered unnecessary and abusive.
Failure to Give the Horse Time to Respond:
Jockeys must allow the horse time to react between strikes.
Rapid-fire whipping is discouraged and may be penalized.