* A misspelling: Perhaps you meant "boom", which is a loud, resonant sound.
* A slang term: It could be a slang word used in a specific community or context. Without more information, it's hard to know its meaning.
* A sound effect: In writing, "thoom" might be used to represent a specific sound like a heavy object hitting the ground or a door slamming shut.
To understand the meaning of "thoom", you need to provide more context. For example, tell me:
* Where did you see or hear the word "thoom"?
* What was the situation or context in which it was used?
With more information, I can help you understand what "thoom" means.