The origin story the name Wittertainment as a reference to the show, as told by Mark, is that Danny Baker used to refer to his own show as "infotainment at it's most infotaining", as he disliked the term "infotainment". Mark and Simon had a conversation about this, and between them decided that they were not "infotainment" but were instead "just two blokes wittering". Subsequently a user wrote in suggestion that "wittertainment" was a better term to use, and it stuck, becoming a short code for the Film Review Show itself and coining the phrase "Wittertainment at it's most wittertaining".
It's use has also spread to be used in the shows social media presence, particularly Twitter and Snaptat.
There was a short lived Wittertainment page on Wikipedia in February 2007 and it's content was as follows:
"Wittertainment is a term inspired by the Good Doctor, Mark Kermode's film reviews on Simon Mayo's BBC Radio Five Live show. Suggested usage: Wittertainment at its most wittertaining
In a nutshell, Kermode, the barrel-chested former Queen‘s guardsman is provoked into ranting by the urbane and erudite Mayo, a perfect foil for the discontemparily-coiffed Kermode. The ensuing witter is surprisingly entertaining. Kermode is undoubtedly a man of many words, a small few of which he unfortunately uses very often. These include, and indeed are exclusively limited to: Guillermo Del Toro, Ken Russell's wife, tertiary syphilis, and some movie called The Exocet, I think.
However, for dedicated pod-casters, Kermode and Mayo cause time to pass unnoticed, a not inconsiderable but much appreciated feat while driving in contemporary urban Ireland."
Unfortunately the Wikipedia custodians decided the page should not survive claiming that "Wittertainment is not a word – I couldn't find it on Google". Interestingly, five years later, a Google search for 'wittertainment' returns over 300,000 results.