A dead drop is a location used to secretly pass items between two people, without requiring them to meet.
Spies have been known to use dead drops, using various techniques to hide the items and to signal that the drop has been made. Drug dealers use this as well.
A common place is to duct tape the item to the underside of a toilet cover in a public restroom.
A signal is sometimes used as well to indicate there is something to pickup, like a pile of stones in a certain formation. After checking the drop the signal is removed.
"The dead drop is the restroom toilet at the Gulf station at the corner of Commercial Ave. and Georges Rd."