An 8-pin connector jack used with standard telephone lines, and required by some ISDN equipment. A little larger than an RJ-11 jack.

The connector on each end of 10Base-T or 100Base-TX twisted-pair cable. RJ-45 connectors are slightly larger than RJ-11 modular telephone connectors and connect eight wires instead of the four used in RJ-11 connectors. RJ-45 connectors snap into the RJ-45 jack on a network adapter card and the RJ-45 port on a network hub or switch.

looks like a telephone connector except that it's larger.