Pre-PC devices had the first-generation user interface -- the command line.

PC devices have the second-generation user interface -- windows, icons, menus and pointing devices (the WIMP user interface).

Post-PC devices have the third-generation user interface -- multi-touch, physics and gestures (MPG).

(Just as there was an awkward overlap between first- and second-generation with first Windows-on-DOS, then DOS-in-Windows, there is a similar transition with multi-touch elements on Macs and Windows 8 PCs.)