A byproduct of cheese making and milk straining. Also used as an exclamation of excitement, most commonly in texts and online messages. The reason people can't just leave a 👍 on the message is unknown.
To be shouted repeatedly whenever elements of lad culture are evident, comments more suited to the FHM letters page than sophisticatedconversation.
lad 1: "So basically, I was completely fucked, y'know, I'd had like, two dozen pints, yeah, and this bird, yeah, she's fuckin' lovin' me, and you know what I did don't ya? I shagged her, didn't I!"
lad 2: "Whey!"
lad 3: "Whey!"
lad 4: "Whey!"
(repeat until no longer funny)