What's the main difference between a "couch" and a "sofa?"

Native speaker’s answer
Rebecca
They mean absolutely the same thing! They both refer to furniture that you can sit on, except "couch" is slightly more casual in feeling. Ex: My new sofa is more of a design piece. It's not very comfortable to sit on. Ex: A: How did you spend your weekend? B: Sitting on my couch, eating pizza.