Well, to me a jumper would be a sweater. When I was a kid, in the sixties, "jumper" was actually the most common word used in the Swedish language for sweater. My mom would say to me, "Ta på dig jumpern", "Put on your sweater". But today "jumper" is a rather unfashionable word in Swedish. Today we would normally say "tröja" instead. (It's pronounced rather like troy-ah".)

Ann