Or 'electric hook-up' for those who don't know much about camping.
In my very early camping days I would quite happily camp with my partner for two or three days without any form of heat or light, but those days were usually restricted to warm and sunny summer weekends; the onset of cooler evenings towards the end of September would signify the end of our camping season, and camping during winter months wasn't even thought of never mind carried out. Fast forward a few years and the eventual purchase of a hook-up cable, a fan heater and a decent light meant that we could camp in a bit more comfort and also extend our season to the end of October if we wanted to do.
Since becoming a solo camper I've camped a few times without electric, but only in summer and mainly because certain places I've been to had no provision for it; normally, whenever I phone a site to book a pitch I always ask for one with electric as it makes my life so much easier and it also means that I can camp in relative comfort during cold winter temperatures if I so wish.
Now I know there are many campers who say that camping isn't 'proper' camping if you have the 'luxury' of electric, but to be honest I really don't see the point in spending chilly days and evenings wearing several layers of clothes and sitting huddled up in a blanket, then going to bed wearing hats and gloves and more layers of clothes - that's not my idea of fun at all. If being able to use a fan heater means I have a warm tent and can go to bed without having to dress like I'm on a polar expedition then it's ehu every time for me.