David P bird wrote : cliques have a limited lifespan
That may well be, but this particular clique has been going strong since, AFAIK, October 21st 2012 with the publication of Dan's first daily puzzle here
So it is well into its 5th year and is still going strong and IMO, keeps the site alive since, sadly, there have been no major solving discoveries for some years and most of the heavy hitters have left, or are at least very quiet.
A tremendous vote of thanks is well overdue to Dan, for his unremitting persistence in posting a puzzle every day since then, for us crazy "clique" members to try and solve in one non-basic move.
stte was mentioned in that thread, so was in vogue at least before Dan started his daily puzzle series. lclste was "invented" by Dan during the currency of the daily puzzle series (see edit below).
I'd be quite happy to see a Sticky that explained what stte, lclste and Basics mean, and what is the "purpose" in solving the daily puzzle in 1 non-Basic move, but I think that would be up to Jason and Dan.
I did a search on stte and found the earliest surviving reference here
on March 4 2009, the "inventor" being DonM.
A similar search for lclste finds the earliest surviving reference here
on January 6th 2013, the "inventor" being Dan (ArkieTech). Dan says that it means "locked cells and sets to end".