If you have experienced a dry-spell in the lady department and get laid unexpectedly, you now have "the scent."
The scent is the confidence achieved from that hookup. You have to take advantage of this confidence booster and find another girl before it wears off, usually two weeks later. If you do land another girl, the scent can keep paying forward.
Nick: I hadn't been laid in 6 months, but last night I got drunk and hooked up with a girl.
Robbie: Oh shit, dude, you better go out on the town every night while you still have the scent or it will be another 6 months for you!