I'm not too sure what it means. I've seen it used in a lot of different contexts, and the most I can gather is that it means something along the lines of, "it's not that". Is this correct, and if not, could someone explain it to me?
An example I saw in the lyrics of a song
そんなかわいいもんじゃないけど 奪わないでいて
もん is short for 物{もの}. That reading is shown under "Other forms" in jisho.org.
The most common meaning for もの is "(physical) thing," but もん is often used on the end of sentences to mean "reason" or "the (hypothetical) thing is," similar to (な)の.
そんなかわいいもんじゃないけど
The thing is, it's not that cute, but...
もん often sounds somewhat childish, petulant, cutesy, or girly.
Here are some other common uses of もん by Maggie-sensei
