The definition of a tie line is a direct connection between two telephone lines in a private network, typically of the same business.
An example of a tie line is a three-digit extension used by employees to call their Human Resources department.
A communications link between extensions of a private telephone system.
A connection between systems, such as electrical power or communications systems.
A direct telephone line between extensions in two or more PBX systems.
A line used to connect one electric power or transportation system with another.
A line that directly interconnects, or ties together, two key telephone systems (KTSs) in a private network configuration, a tie line is a dedicated circuit that generally is leased from a public carrier. A tie line allows users to avoid toll charges for long-distance calls between two geographically separated offices. If a key system sits behind (i.e., is used in conjunction with) a PBX, one or more tie lines are used to interconnect them. See also line, nailed-up circuit, and tie trunk.