Telephone tapping is the monitoring of telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 and Internet

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 conversations by a third party, often by covert means. The wire tap received its name because, historically, the monitoring connection was an actual electrical tap

Tap (transformer)

A transformer tap is a connection point along a transformer winding that allows a certain number of turns to be selected. This means, a transformer with a variable turns ratio is produced, enabling voltage regulation of the output...

 on the telephone line. Legal wiretapping by a government agency

Government agency

A government or state agency is a permanent or semi-permanent organization in the machinery of government that is responsible for the oversight and administration of specific functions, such as an intelligence agency. There is a notable variety of agency types...

 is also called lawful interception

Lawful interception

Lawful interception is obtaining communications network data pursuant to lawful authority for the purpose of analysis or evidence. Such data generally consist of signalling or network management information or, in fewer instances, the content of the communications...

. Passive wiretapping monitors or records the traffic, while active wiretapping alters or otherwise affects it.
Telephone tapping is officially strictly controlled in many countries to safeguard privacy

Privacy

Privacy is the ability of an individual or group to seclude themselves or information about themselves and thereby reveal themselves selectively...

; this is the case in all developed democracies

Democracy

Democracy is generally defined as a form of government in which all adult citizens have an equal say in the decisions that affect their lives. Ideally, this includes equal participation in the proposal, development and passage of legislation into law...

.