Good question. NCLT stands for non-circulating legal tender. It means the same thing as pseudo-coins and medal-coins: coins that don't circulate. The term was invented by Krause and Mishler, who are between the ire of advanced collectors and the sensitivities of advertisers, often the issuers of NCLT. KM probably thought NCLT would be neutral, but that was of course wishful thinking, as any label of something ugly will become ugly.
The legal tender part has created much confusion. There is a tribe of collectors proclaiming that coins must be legal tender (which ought to exclude all classical coins, al primitive money and quite a few other legitimate coins, but includes pseudo coins as coins). NCLT issuers happily mention that their wares ae legal tender as a sales argument. See for instance
this thread, where an absurd piece is offered as "legal tender". Therefore, I don't think NCLT is a helpful term.
Peter