It's a male panel mount 8-pin mains connector from bulgin. It probablly has multiple uses in different applications but the one i'm aware of is as an inlet on boxes with multiple lights to connect them to a light sequencer. I don't remember the exact part number offhand.
I would advise against using the terms plug and socket when talking about such connectors as they are likely to confuse.
Older kit used female connectors on both the light sequencer and the light box and then used a male to male cable to connect them together but that was later deemed unsafe.
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