Conventional (Enhanced) layouts are those used by the 101/102-key Model M, and by most keyboards today, as well as slight variations on those layouts (differently shaped enter keys, Windows keys, that sort of thing).
Extended conventional layouts add dedicated media, macro, and/or extra function keys. The media keys are popular on consumer boards, the macro keys are popular on gaming boards, and the extra function keys used to mainly be on terminal keyboards.
Tenkeyless layouts remove the numeric keypad, but leave the navigation cluster and function keys.
Navigationless layouts with tenkey remove the arrow and other navigation keys (Insert/Delete/Home/End/PgUp/PgDn), but leave the numeric keypad. Not common nowadays, but Cooler Master has one board with such a layout, and the IBM PC, PC/XT, and PC/AT keyboards had such layouts.
Compact layouts are a tenkeyless layout that is extremely condensed, like a laptop keyboard. Some even leave off dedicated navigation and function keys entirely, like the Happy Hacking Keyboard and other "60%" layouts.
Fixed ergonomic layouts are those with a split in the main typing area to prevent your wrists from rotating, and may have other shape differences as well. The Microsoft Natural keyboard is the example that's typically given in this case.
Adjustable ergonomic layouts are those that can have their split angle adjusted, and may have other adjustments as well.
Last edited by bhtooefr
on Wed Jul 10, 2013 10:23 am, edited 1 time in total.