On the keyboard. I do remember as a very young lad there being a Return key on the computers. Like a typewriter had. Somewhere along the line that became the Enter key. But damned if I can put my finger on when it happened.
I think it was an IBM PC thing. Looks like the original IBM PC (1981) has a "return-like" arrow, but the PC/AT labeled the key "enter." IBM PC keyboard - Wikipedia
Apple keyboards still say "return" (some of them say "enter" as well.)
Ballscrewbob:
Or about the same time "SCREEN LOCK" found a smart phone and became "scrlk" etc etc...
But it's always been an abbreviation for "Scroll Lock". I think the only program in widespread use that uses it is Excel and it really confuses people when they hit it accidentally. Everything else works fine except for Excel.