This is a fully rubberised socket on a very short cable to an IEC plug.
What's it for? Essentially, if you want an Uninterruptible Power Supply for your computer, hard drives or other always-on equipment, you either need to buy one with IEC sockets or one with UK mains sockets. The mains sockets type are more bulky, and tend to be available only in smaller capacities. Typically only half of the sockets are UPS, and the other half are merely surge protected. The larger and more powerful type are usually IEC only. However, if you want to connect non-IEC equipment, such as Time Capsule or an external hard drive, you'll find these have figure-eight cables, not IECs. You can make your own IEC to figure-eight cables, but it's more convenient and reliable to buy these. They are rugged and do the job, and, of course, allow you to plug anything in, not just figure-eight equipment.