It's a word that shows the relationship between other words in a sentence, like "He is among the crowd."
Here's how to think about it:
* Common Nouns: Name general things or people (e.g., dog, city, teacher)
* Proper Nouns: Name specific people, places, or things (e.g., Fido, Paris, Mr. Smith)
Since "among" doesn't name anything, it's not a noun at all.