Small bumps on certain keycaps to keep touch-typists registered.
Usually on the 5 of a numeric keypad, and on the F and J of a
{QWERTY} keyboard; but older Macs (like pre-PC electric typewriters)
had them on the D and K keys (this changed in 1999).
[glossary]
[Reference(s) to this entry by made by: {pastie}]