Using a common friend as a secondary way to communicate to your girlfriend/boyfriend the things that are uncomfortable for you discuss directly with your girlfriend/boyfriend.
"Hey Steph! You're my back channel! What does Lisa like as far as engagement rings go?"
by Flacker January 15, 2007
Getting someone's personal contact information so you don't have to communicate with them through a public means.
We were having a conversation on a public web site, but I wanted to backchannel her so we could get more personal.
by Biggety Big September 17, 2006