tie line

WordReference Random House Unabridged Dictionary of American English © 2025

tie′ line′, [Telecommunications.]

1. Telecommunications a line that connects two or more extensions in a PBX telephone system.
2. Telecommunications a private telephone channel, leased from a telephone company, that connects two or more PBX systems.

Collins Concise English Dictionary © HarperCollins Publishers::

tie line noun

1. a telephone line between two private branch exchanges or private exchanges that may or may not pass through a main exchange