An existential clause is a °clause construction in which an °indefinite nominal is said to be in some location.
The definition is from Haspelmath (2025: 18). The nominal that is said to be in some location can be called "existent" (another term found in the literature is "pivot").
Note that the location can be implicit (and inferred from the context), but that "pure existence" is not included in the definition here (it is called "tautotic").
Since existential clauses are not really about "existence" but rather about location, Creissels (2019) proposes the term "inverse-locational" (at least for a subset of existential clauses, those that have "special syntax"). See also Creissels et al. (2016: §4.4).
existence event (SEM) = a situation in which the existence of some entity is presented. Existential situations favor a thetic construal. Example: There are apples in the kitchen expresses the existence of the relevant set of apples. (Section 11.3.1)
"Though the term “existential sentence” goes back at least as far as Jespersen (1924: 155) and is used in descriptions of many languages to refer to a designated construction, it is difficult to identify exactly what these constructions have in common crosslinguistically. Following McNally (2011: 1829), the term is used here to refer to sentence types that are “noncanonical,” whether due to some aspect of their syntax or the presence of a distinguished lexical item (e.g., Spanish hay) and that are “typically used to express a proposition about the existence or the presence of someone or something.” " (McNally 2016: 2011)