A woman's control over when, where and how sex will be had. Analogous to "purse strings" but pertaining to the pussy.
"Ever since I bought my girl friend something in a little blue box from Tiffany's and she has really loosened the puss strings"
"My wife totally tightened the puss strings when she found out I charged a new surfboard for my trip to Fiji."
He may wear the pants in the family but his wife still holds the puss strings."