I was chatting on the internet and the term was used in response to a question that I had but the person was unable to explain the term to me. I am thinking that it may be an abbreviated form of ふうんいき。Thank you.
No, it is not. We don't reduce 雰囲気 to ふうん.
ふうん is a sort of filler meaning 'I see/ uh-huh/hmmm/really?/for real?/I don't care/how dare you/etc.
When it's actually spoken, the meaning of a ふうん or ふーん can vary very widely depending on the tones and context. On the other hand, written ふうん/ふーん on the internet generally means 'ic.'( I see.) unless it's not in a quotation.
I'm not enough adept at scripting an answer to show the subtle tones and nuances, let me look up for a video that explains well about variations of ふーん/ふうん。
I found a video that epitomises ふーん for meaning 'how dare you say such a thing!'. It's hilarious actually that I want to share with you.
The male MC Mr. Shimoda reads a letter from a listener dubbed himself 'Koharungo2'.
The letter begins with 'Hello Mr. Shimoda and Ms. Tadokoro. I know this is sudden but I love boobs.' Then Tadokoro who's known for her huge tits response with a consummate ふーん。 This is it.