10base5 and 10base2 Local Area Networks (LANs) are normally configured in a bus configuration. Both ends of the coaxial cable used as the bus medium require terminators. These LAN cable terminators are impedance matched to the cable, normally 50ohms.

                 node1       node3
                   |           |
          X------------------------------------X
     terminator          |            |    terminator
                       node2        node4

The terminator is used to create a complete electrical path from the center conductor to the outer shield. The 50ohm resistor built into the terminator absorbs signal reflections.