Reference and Inference
Reference of Indefinite Noun Phrases
Have a look at the following three sentences and figure out the difference between the referring expressions (the noun phrases) set in boldface:
a. There's a woman waiting for you.
b. She wants to marry a man with lots of money.
c. I'd like to see a unicorn.
You can find an answer to this task on the page Referential and Attributive Use.