Dangle (podstava in Russian intelligence jargon and chèvre in French police and intelligence jargon) is a term used in intelligence work to refer to an agent or officer of one intelligence agency or group who pretends to be interested in defecting or turning to another intelligence agency or group.
The goal of a dangle is to convince the second or foreign intelligence agency that they have changed loyalties by offering to act as a double agent. The dangle then feeds information to their original agency and/or gives disinformation to the second or foreign intelligence agency.
References
Dangle (espionage) Wikipedia(Text) CC BY-SA