A "pigeon drop" is a confidence trick in which a mark or "pigeon" is convinced to give up a sum of good-faith money in order to secure the promise of sharing a larger amount of "found money".
Ultimately, the scammers disappear with the good-faith money and "drop" the mark who is left holding a worthless bag, wallet or envelope filled with news clippings cut into the shape of previously observed currency.
Expectation of new-found wealth from questionable source, even one amicably shared, is soon replaced with unexpected loss of existing assets.
related: What does the phrase or term pigeon drop fraud mean?
See also Pigeon Drop Scam, Jamaican Switch Scam, Latin Lotto, South African Switch, Credit Card Liability