Postdigital or post-digital is a somewhat misleading concept but may be useful for understanding some phenomena in today's world.
The "digital" in "postdigital" is to be read a bit like the "modern" in "postmodern": it refers to a very specific kind of "digital", a highly technoprogressivist and industry-defined kind that became prominent in the "digital revolution" hype of the 1990s. This is also why even some profoundly digital things such as pixel art and digital glitches have been labelled "postdigital" in artistic circles.
When distancing itself from this kind of "mainstream digitality", "Postdigital" also distances from many of the destructive ideas whose abolishment is also relevant to permacomputing (maximalism, ?virtualism, obsolescence, etc).
"Postdigital" is also a reaction to the digital oversaturation. Computers are no longer "inherently cool" (like many people born in the 1970s and 1980s found them), but now the same kind of coolness can be found in non-digital things such as physical and analog artforms – or things that are digital in alternative and countercultural ways (like permacomputing is).