Telephone Terminology

Below are definitions of terms commonly used in the telephone industry. This list is not designed to be comprehensive, but rather to give a basic definition. Some of these terms have specific regulatory or technical definitions as spelled out in law or statute. In those situations, the legal or technical definition takes precedence.


Bandwidth: The range of frequencies available for signaling.


Baud: A unit of signaling speed equivalent to the number of signaling elements per second.


Byte: A group of binary digits which are processed by a computer as a unit.


Central Office: A building that houses telecommunications equipment.


Circuit: The physical connection of channels, conductors and equipment in such a way as to provide discrete communications between two given points. A circuit is comprised of both a sending line and a receiving line.


Circuit Grade: The information carrying capability of a circuit in terms of speed or type of signal.

Competitive Local Exchange Carrier (CLEC):

A competing company that is licensed to provide local telephone service using their own network or a portion of the network owned and installed by another company. CLECs provide service in competition with the Incumbent Local Exchange Carrier or ILEC.


Cramming: The unauthorized addition of services or features to your telephone service. These services may be such things as voice mail, caller ID, special service packages or fee-for-service charges such as 900 calls.


Cross Connection: A term used to indicate the actual tying together of telephone equipment in the central office.


Crosstalk: The unwanted blending of noise, conversation or audible interference that is typically caused by two lines touching one another.


Exchange: A geographic area established by the incumbent local service provider usually encompassing a city, town, village or surrounding areas. It consists of one or more central offices together with the associated equipment used in furnishing communications service.


Exchange Service: A service permitting interconnection of any two customers' stations through the use of carrier provided common equipment.


Extended Area Service: A telephone exchange service that extends over a usual boundary to contiguous areas, without toll charges. This exists in areas where there is a community of interest and toll charges are not applied in return for a somewhat higher basic exchange service rate.


Facsimile: The transmission of pictures, maps or other documents via communications channels by means of a device which scans the original document and transforms the message into coded signals.


Filter: A circuit or device which eliminates a larger proportion of unwanted frequencies than it does desired frequencies. Typically, filters are used on a communications channel to guard from adjacent channel interference.


Frame: An amount of information within a defined boundary.


Frequency: The rate of signal oscillation measured in hertz or cycles per second.


Hertz: A unit of frequency expressed in cycles per second. One hertz equals one cycle per second.


High Pass Filter: A wave filter which screens out all signals below a predefined limit and allows all signals above that limit to be received by a unit.

Incumbent Local Exchange Carrier (ILEC):

Interactive Voice Response Unit (IVRU):

Automated electronic or software devices that give callers the option to press a number to route their call to a specific destination, enter account numbers or enter information that assists a company in serving the end user.
The company that owns or controls the network of wires and switches used to deliver phone service in your area.


Intercept: The rerouting of a telephone call to a recorded message, operator or other device.


Interconnect: To connect privately owned components to a public network of communications common carriers.


Interface: The mechanical or electrical shared boundary or link connecting two or more physical entities or systems.


Interstate: Telephone calls originating in one state and terminating in another.


Intrastate: Telephone calls that originate or terminate in the same state.


Jack: The physical connecting device at the interface which mates with a compatible receptacle.


Loop: The wires that extend from the local telephone company's central office to the customer's premises.


Modem: A device which modulates and demodulates signals transmitted on a carrier frequency. Through this process digital signals can be translated into analog signals and sent through communications networks.


Noise: Any interference or unwanted signal which disturbs the quality of the signal being received.


Numbering Plan: A uniform system for assigning numbers to every terminal on the national network so that each can be reached through direct dial numbers. The first three are the area code and the second three designate an exchange within the dialed area.


Off Hook: To activate a telephone unit by lifting the handset from it's cradle.


Operator Assisted Calls: Any call which requires the assistance of an operator employed by the telephone company. Types of operator assisted calls include collect and credit card calls.


Person-To-Person Call: An operator assisted call in which the calling party specifies the person with whom he/she wishes to speak. If the called party is unable to accept the call, there is no charge to the party who initiated the call.


Premises: A home, business or dwelling where service originates and/or terminates.

Relay Service:


Slamming occurs when a company changes your local or long distance service without your consent.
A service that allows the hearing community to communicate with the deaf or hard of hearing via an operator who uses a keyboard device to transcribe what one person says. The hearing impaired individual can read the conversation on a screen.


Substation: Any additional station which has been established as an extension to the primary line.


Switching Center: An automatic, semiautomatic or manual location that terminates multiple circuits and is capable of interconnecting circuits or stations or transferring traffic between circuits or stations.


Tariff: The schedule of rates and regulations pertaining to the services of a communications common carrier. Tariffs are filed with the appropriate regulatory agency.


An acronym for Telecommunications Device for the Deaf, which are electronic devices that allow the hearing impaired to communicate over the telephone using a keyboard-based device.


Telecommunications: The science and technology of transmitting information or data over a network using electrical or optical impulses.


Telephone: The generic term for handset equipment capable of acting as a terminal point on a voice grade channel.


Toll Restriction: A limit initiated by the customer or the telephone company whereby the customer cannot make toll calls.


Toll Trunk: A communications channel between a toll office and a local central office.


Traffic: The volume and intensity of transmitted and received messages over a communications network.


Transmission: The passage of information through a communication medium.


A term derived from the registered trademark of the Teletype Corporation. This term has commonly used in reference to teleprinters used by the deaf and hearing impaired. Similar to TDD devices.


Voice: Pertaining to human speech and any device capable of using human speech in its designate function.


Voice Connecting Arrangement: An interface arrangement provided by the telephone company to accommodate the connection of non-carrier provided voice terminal equipment to the public switched telephone network.


Voice Grade: Pertaining specifically to any means of transmission of speech or any channel, which is capable of transmitting human speech.