It is called "existential clause", "existential sentence", or "existential construction" or simply existential.
This terms refer for all tenses of the existential clauses, such as: there is, there are, there was, there were, there will etc.
Existential (n. & adj.) (A grammatically *marked *structure) typically
used to express a *proposition that someone or something exists.
An existential *construction (also called a there-existential) typically
conforms to the following pattern:
there + (auxiliary / raising verb) + be + notional subject.
The unstressed *pronoun there is a *dummy subject called existential
there. Here are some examples:
There is an emergency
There must be a God
There seems to be no solution
These are called bare existential clauses, which do not have a
nonexistential counterpart (cf. *An emergency is).
An extended existential clause contains additional material
(called the extension), such as a *locative (1) or *temporal phrase, a
*relative clause, a *to-infinitive, or an *-ing clause:
There is a mouse in the loft
There was a fire last week
There has been nothing in the papers about this
Can there be life on other planets?
There’s one student who brings her dog to class
There is a great deal of work to do
There was a fox running down the street
(The Oxford Dictionary of English Grammar. P.147)