balanced connection   

Indicates 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.