Clopping

Clopping is the onomatopoeic sound of a horse's footsteps, or hoofbeat.

In the My Little Pony: Friendship is Magic fandom, "clopping" is a euphemism for masturbation, similarly to the furry fandom's use of the phrase "pawing off".

Adult artwork featuring Friendship is Magic characters is sometimes referred to as "clop".

Clop