existential "it"
Definition - Using it instead of there to show something's existence instead of its location.

Example -
Saying "It was nothing I could do" instead of "there was nothing I could do."

Quotation -
"Existential it is hardly a recent innovation — it appears in Middle English; in Elizabethan English, as in Marlowe's Edward II: “Cousin, it is no dealing with him now”; and in modern American literature as well."
(Source: http://www.bartleby.com/61/94/I0259400.html )

Please comment