Dictionary.net

A telephone line leased expressly for thepurpose of connecting two users more-or-less permenantly..Such lines may be "voice grade" which provides the bandwidthand signal to noise ratio of ordinary public switchedtelephone network circuits, or specified in ways which allowtransport of suitably encoded digital signals at faster rates.In some cases, lines may be physical wires between thecommunicating parties. Over longer distances, it is commonfor the connection to be virtual, which means that althoughthe two users can communicate only with each other, theirsignals and others are multiplexed, amplified, switched,scrambled, demultiplexed and so on in complex ways between theend points.This contrasts with a dial-up connection which is onlyopened when one end requires it.