Hello, I was wondering what a pet rating was. Is it something where someone rates your pet, or is it a battle thing? Thanks for your help.

I think you're talking about the blue building? When it says pet rating of 100 or more, it means the overall stats of one of your pets has to be 100 or more. For example if you had 25 strength, 25 defense, and 50 hp. I think the level and intelligence counts too?

Level counts, Intelligence does not.