Mystery Science Theater 3000 is a geek institution (with “MSTing” entering the vernacular) for good reason. The original television show is, when you get down to it, a variant on the time-honoured tradition (which I believe to be distinct to America) of having televised genre movies in a special slot with host segments introducing the movie and maybe breaking in with little skits. This is an approach which started with Vampira – yes, the one from Plan 9 From Outer Space in the 1950s – and continued through Elvira and others up to the present day.
The MST3K difference is that the host doesn’t go away – whereas most horror hosts of yesteryear clear off for the actual movie, MST3K has its host (and their robot friends) appear in a silhouette of cinema seating at the base of the screen, cracking jokes about the (usually terrible) movies featured on the show. Anyone in fandom who has not seen the show – which is now easier than ever to access outside of its US stamping grounds thanks to YouTube and various other platforms – at the very least has reasonable odds of recognising two things: the term “MSTing” and the theatre silhouette.
Since the original run of the show closed out at the end of season 9, various “movie riffing” outlets have tried to continue this approach, with or without the silhouettes; The Rifftrax project spearheaded by Mike Nelson, final host of the original show, hit on the idea that if you went without the silhouette and just sold an audio file that people synced up with their copies of the movie being riffed, then a world of copyright headaches could be avoided. Joel Hodgson, creator of the show and the original host, established Cinematic Titanic, which tried to incorporate a few more comedians in the riffing crew with a redesigned silhouette in its first few episodes (released direct to DVD in a world where, already, some form of streaming or download setup would reach more customers), before shifting to a live show format which went without the silhouettes (because what would be the point of including them in a show where you can see the riffers onstage anyway?).