What is a long gun & how does it differ from a rifle?

I saw a security footage
of a guy robbing a store with a “long gun”. It looked like a rifle to me; so, I started googling. The results clearly explained the difference between a long gun & a hand gun. I never discovered the appropriate search query to get my answer. Wiki had a piece on “long guns” but the description sounded like they were describing a rifle to me. It drives me crazy to not be able to find the answer to what I want to know. So, can you explain to me the difference between a “long gun” & a rifle???