It's possible that:
* It's a misspelling: Perhaps you meant a different word, like "most likely" or "mastering."
* It's a proper noun: It could be a surname or a place name.
* It's a technical term: It might be used in a specific field or industry.
Could you please provide more context? For example:
* Where did you encounter the word?
* What was the surrounding text or conversation?
With more information, I might be able to figure out what "mosteling" means.