From the ARRL “So What” podcast
All about the Coax Cable
Regardless of whether you are operating at HF, VHF or UHF, the quality of your feed line is critical to your station. The feed line (also called the transmission line) is the RF power conduit between your radio and your antenna. All the energy you generate travels to the antenna through the feed line. By the same token, all the signals picked up by your antenna must reach your radio through the same feed line.
Read the rest on the ARRL Website
Wikipedia Artical: Coaxial Cable info