Embroidery Only machine are just that. They don't usually have feed dogs and often have multiple needles so you can thread them up with several colors and walk away.
I don't know if you can do FMQ on one of them, but you can't do any piecing on it. Most people buy combination machines, there is a limited market for embroidery only - and a lot of that is business.
I think most people refer to machines as "embroidery" or "embroidery only". Rarely does anyone call them "combination" machines though that is what they are - they sew and embroider.