Pet the horse in chat??

Hey yall, this is a totally stupid question but I’m way too curious so I’m asking anyways. When people put “pet the horse” after their messages in chat, what does that do??
Somebody in global told me it was to get around the system, but I feel like you guys can maybe give me a more specific answer lol.
(I’ve been playing for eleven years but rarely ever opened the chat and every time I do it’s like a different language 😩😩 there’s so many abbreviations I just have no idea about lmfao)