A transmission line carries radio-frequency energy between components. In an amateur radio station, the line connecting a transceiver and an antenna is commonly called the feed line.
Coaxial cable is widely used because its shielding and routing are convenient. Balanced lines are another option. The suitable line depends on frequency, the installation and the equipment being connected.
Loss, characteristic impedance, connectors and weather protection affect the complete system. The length and condition of the line should be recorded when reporting antenna measurements.
A low standing wave ratio is useful, but does not by itself establish antenna efficiency or low feed-line loss.