I have been looking into home recording and have come across something I don't understand. What is the definition of an external sound card, and what makes it different than an internal sound card? I ask because I have heard several people refer to USB audio interfaces as "sound cards". When I type "external sound card" into Sweetwater's search, it takes me straight to the audio interfaces page. It seems to me that sound cards and interfaces are two very different products. I come to TB for answers.