Jumper; Figure 2-4: An Example Of Three-Pin Jumper Setting - Datatech Enterprises Apex 386SX/20 User Manual

Jumper

A jumper is a kind of switch which uses a plastic cap with a metal
interior to connect (short) two pins. If a jumper needs to be left open,
you should save the cap for future use by covering only one pin of a
jumper. This has no effect on the function of the board while it keeps
the cap handy. The illustration below shows the side and top views of
a three-pin jumper in which pins two and three are shorted.

Figure 2-4: An Example of Three-Pin Jumper Setting

Chapter 2: Setting Up Your System
7