* A misspelling: Perhaps it's meant to be something like "LMAO" (laughing my ass off).
* A specific in-group slang: It could be a term used within a particular community or online group.
* A made-up word: Some people invent their own slang.
To understand what "LYAO" means, you need more context. For example:
* Where did you see it? (online forum, chat, text message)
* What was the conversation about?
* Who was using the term?
With more information, I might be able to help decipher the meaning.