* It's a typo: Perhaps you meant a different word, and a letter was accidentally omitted or replaced.
* It's an abbreviation or acronym: Could it stand for something specific within a particular field or context?
* It's a slang term: It might be a slang word used in a specific community or online group.
* It's a made-up word: It's possible it's a word someone invented for a specific purpose.
To figure out what "Nmao" means, you'll need more context:
* Where did you see or hear it?
* What was the surrounding text or conversation?
* Who said it?
Providing more information will help us understand the intended meaning.