Weird, wet spot on my cat

[alma8mater]

A week or so ago, my cat came home (because he normally wanders outside and has his own journey) and there was this weird, wet spot on his fur. Like I can’t dry it, and it looks to be parted apart to show his skin. He came again today, and that spot was still there, luckily I have a picture. I want to just make sure it’s not anything super bad and a way to treat it

 

[Antonio65]

Is it greasy, oily? Does it have a smell?
Just in case, do not allow your cat lick that wet stuff off his fur.
Can you bathe him? Or have him bathed?