Social Anxiety?

What is social anxiety? How does it differ from other anxiety disorders? I was wondering, because I'm 17 , and I've never been outgoing and I've always been super shy. I always thought it was just shyness, but talking to other shy friends, I realized mine is extreme and causes me physical symptoms that don't go away For example, whenever I have to eat food in public or ask for something I get super nervous and panicky and won't eat food. I had to order food yesterday, and I knew what I wanted but when I went up to order I panicked and instead only got water. Also, if I'm around a lot of people I freak out. I had to be in a room today with a lot of people, and it was so overwhelming that I couldn't breathe, my heart started to race, I got sweaty and I had to leave and wasn't able to go back in.