Petrichor is, defined by Idris, the smell of dust after rain. Idris used the word "Petrichor" as part of the key to open a back-up TARDIS control, which she gave to Rory through a telepathic link. (DW: The Doctor's Wife)
Petrichor is also the name of a fragrance company that Amy Pond worked for as a model. Its slogan was "For the girl who's tired of waiting." This modelling job with Petrichor apparently made her rather famous. (DW: Closing Time)