What is the difference between an RJ-45 connector and an RJ-45 socket, and why does proper termination matter?

The connector is the male plug crimped onto the cable; the socket is the female port on a device or wall jack. Termination matters because untwisting the pairs near the plug lets in interference.

The two halves of the same connection are easy to confuse:

• RJ-45 connector — the male plug crimped onto the end of a UTP cable.
• RJ-45 socket — the female port that the plug pushes into, found on switches, computers, and wall jacks.

Why termination quality is critical comes straight from how UTP works: the cable fights interference only through its twisted pairs (it has no shielding). To crimp on a connector you have to untwist the pairs a little — and every millimetre of untwisted, exposed wire is a spot that can pick up noise and crosstalk. A poorly terminated cable leaves too much wire untwisted; a properly terminated one keeps the twist as close to the connector as possible, so the noise cancellation holds right up to the pins. This is why poor termination is one of the most common sources of intermittent network connectivity problems.

Go deeper:

• 8P8C / RJ-45 modular connector — Wikipedia — the male plug (and its mating jack), with pinout and termination detail.

• Crosstalk — Wikipedia — the noise that untwisting at a poorly terminated plug lets in.