three contacts: hi, low & ground. Usually
uses an xlr or “Canon” connector or a tip/sleeve/ring phone connector.
Usually a low impedance connection (150-600 ohms).
Any cable will act as an antenna. By comparing signals in the low & hi cables, balanced cables or connections can eliminate rf or radio frequency interference.
|Illustration is of standard balanced connectors called XLR or Canon. Term comes from “balanced differential input” which is a more precise description of how it works.|