OWO means two completely unrelated things, and which one you want depends entirely on where you saw it. Most people searching for this want the first one.
The internet one: OwO
Written with a lower case w between two capital letters, OwO is an emoticon. The two O shapes are wide eyes and the w is a small mouth, so the whole thing reads as a startled or delighted face. It spread through anime, furry and gaming communities and is now general internet shorthand for surprise, excitement or mock innocence.
You will see it in usernames, chat, comments and captions. There is a related form, UwU, which reads as a contented face rather than a surprised one. Neither has anything to do with the second meaning below, and seeing it in a game chat is not a signal of anything.
The dating and listings one: OWO
In dating profiles and escort listings, written in capitals alongside other abbreviations, OWO stands for oral without. It means oral sex performed without a condom, as opposed to with one.
It appears in that context because listings are written in a compressed shorthand inherited from old forums, where plainer wording ran into advertising filters. The habit stuck. If you are reading a listing full of acronyms, this is the meaning in play.
Why it is listed at all
Because it is a meaningful distinction to the people involved, and stating it up front saves an awkward conversation later. It also carries a real difference in risk, which is the part worth understanding rather than skipping.
Unprotected oral sex carries a lower risk of transmitting HIV than unprotected intercourse, but it is not no risk, and it transmits several other infections including gonorrhoea, syphilis, herpes and HPV reasonably efficiently. Anyone making decisions here should be doing so with current information from a sexual health service rather than from a directory, and in the UK that service is free and confidential through NHS sexual health clinics.
Reading it in a listing
Treat it as you would any other abbreviation: a signal of roughly what is on offer, not a contract. Nobody governs these terms and nobody is obliged to mean the same thing by them. Someone listing it today may not be offering it tonight, and that is entirely their call.
Ask once, plainly, when you make the booking. Do not push, and do not treat a listing as an agreement already made. The booking guide covers the wording that gets a straight answer.
The other abbreviations
OWO usually appears alongside several others. GFE describes a warmer, unhurried register and PSE the more intense end of the same scale. The glossary covers the rest in one place.