2. Meta Language. R. Milner <firstname.lastname@example.org> et al, 1973. A strict higher-order functional language. It was the first language to include polymorphic typing which was statically-checked. It also had garbage collection and a formal semantics.
It began as the metalanguage for the Edinburgh LCF proof assistant. (LCF="Logic for Computable Functions") People soon noticed that ML could be a useful general programming language and stand-alone versions were implemented. Standard ML (SML) is a descendant of these (and related languages such as Hope).
The "metalanguage" aspect has long since disappeared from the language itself (although there are some systems that still use it that way). The historical name is now so inappropriate that asking what ML stands for is like asking what C or Unix stands for. It doesn't stand for anything; it just is.
The country code for Mali.