Expletive noun phrase

An expletive (noun phrase) is a noun phrase (mostly a pronoun-like element) that occupies a syntactic position, but has no semantic role.

Expletive is a grammatical element having no semantic content and occurring in theta-bar positions.

Examples
The best-known expletive is the English it in ambient constructions like it is raining, and in extraposition constructions like It is nice that you managed to come.

there in (i) and it in (ii) are expletives.

(i) There is a man in the room (ii) It seems that John is ill

Synonym
dummy noun phrase

Origin
This usage seems to date only from the 1970s.

Link
Utrecht Lexicon of Linguistics