Afghan originates from the word Afghanistan. The country is known for it’s colorful carpets, and beautiful wool, so “afghan” was what people called knitted or crocheted blankets.
Afghan is tossed around with the words “throw” and “blanket” a lot. They mean pretty much the same thing.
For me, an afghan is something that is more decorative than used as an actual cover. I have seen crocheted or knitted afghans as a bedspread and that works too.