Wiretapping is secretly listening to other people's phone calls by making a connection to their phone line. The classic picture is police or government agents in a van, or a detective in a film, quietly hearing every call a suspect makes without the suspect knowing. Today the actual wires often are not there — calls travel through phone networks and the internet — but the word has stayed and now covers secret official listening in general, including reading messages. Some of the important ideas live in the words around it: a wiretap (noun) is one particular act of listening, or the equipment used for it; to tap someone's phone is the verb; and a wiretapping warrant is the paper a judge signs to make it legal. Legality is really the heart of this word. Most of the time you meet wiretapping in news, court, and politics, and the question being argued is whether it was allowed. Wiretapping without a warrant is a crime in many countries, so the word usually arrives with a whiff of scandal or of serious police work. It is a formal-ish, written word; a friend telling a story would more likely say they tapped his phone.