In regard to computers, a Jumper is a Shunt, and they will normally be found
on motherboards and add-on cards.
So a Jumper on a motherboard or add-on card (video, sound, etc.) is a small
shorting device that makes a connection between 2 pins.
For additional info, including pictures, do a Google search. You will get
plenty of hits.
By the way, many of the newer motherboards and add-on cards contain no
jumpers. Most computer builders like this, because there are fewer things
they can do wrong.