Look and feel
How an interface looks and how it behaves, treated as a thing that can be standardised, licensed, copied and, for a few years in the late 80s and early 90s, litigated over.
The phrase took hold once graphical interfaces became a market. The look is the visual part — the bevel on a button, the shape of a scrollbar, the palette — and the feel is the behaviour: which mouse button opens a menu, how focus moves, where you drag to resize. The Unix wars were fought explicitly on that front. In 1988 OSF issued a "Request for Technology" for a look and feel and chose the HP and Microsoft proposal, a relative of Presentation Manager, which became Motif. Sun and AT&T answered with OPEN LOOK, a pure specification of appearance and behaviour with several implementations. Motif won for reasons that had more to do with who stood behind it than with which was better.
The question was tested in court at the same time. Apple sued Microsoft and HP in 1988, claiming Windows 2.0 and NewWave had copied the Macintosh look and feel, and lost in all essentials by 1994, when the courts found that individual elements such as overlapping windows and trash cans were not protected. Lotus v. Borland, over Quattro Pro's copy of the 1-2-3 menu tree, ended in 1996 with menus classed as a method of operation rather than a work. The League for Programming Freedom was founded in 1989 to protest against precisely these cases. Once the smoke cleared, look and feel became something you swapped instead: Java Swing shipped its pluggable look and feel in 1998 with Metal, Motif and Windows as options, Winamp and Enlightenment turned skins into a subculture, and GTK and Qt let a single theme change everything at once.