Eavesdropping is the act of surreptitiously listening to a private conversation.
Ancient Anglo-Saxon law punished eavesdroppers, who skulked in the Eavesdrip of another's home, with a fine.
Eavesdropping can also be done over telephone lines (wiretapping), email, instant messaging, and other methods of communication considered private. (If a message is publicly broadcast, witnessing it does not count as eavesdropping.)
In ancient China, it is said that to prevent eavesdropping when discussing important matters, soldiers would instead draw the characters on hands or papers. This is where the superstition of the "black dot" on a piece of paper comes from.
The Canadian heroine Laura Secord is famous for having eavesdropped on the plans of the American army and delivering this information to the British during the War of 1812.
Eavesdropping is something of a clichéd plot device in fiction, allowing the hero or villain to gain vital information by deliberately or accidentally overhearing a conversation. For instance, in "Letting In the Jungle" by Rudyard Kipling, Mowgli overhears the hunter Buldeo telling some men that Mowgli's adopted mother Messua is about to be executed, so Mowgli sets about rescuing her.