There's "this" boy/girl/guy

Question

Is the phrase "there's this + noun" as in "There's this girl I met yesterday ..." a discourse marker? If not, what is it considered to be in grammar terminology?

Answer 1

There's this girl I met yesterday.

There is nothing non-standard about the use of there's here; the sentence would have much the same sense if it were spoken "There's a girl I met yesterday". What is unusual is specifically the use of this. CGEL (17.5.4(b), p. 1510) gives some examples:

 ^%He's been married and got this half-grown kid.
 ^%I was in Penang and I met this man, and he gave me your address and a present for you.
 ^%She was wearing these enormous earrings that she'd bought at the duty free.

The demonstrative NPs here are false definites in that they have the form of a definite NP but do not satisfy the conditions for the felicitous use of one. They introduce new entities into the discourse and do not have sufficient descriptive content to identify the referent for the addressee. This usage is characteristic of very informal conversation, ...

I'd go a little further than CGEL. To me the colloquial this is not a false definite—the speaker has a very particular kid, man, pair of earrings in mind, and usually the object indicated will have some further role in the discourse—but a false reference—the kid, man, pair of earrings are not present. But if they were present, the speaker could and would point them out with an ordinary this.