Unofficial means of communication, and a hint to each set of circled letters

• Unofficial means of communication
• Covert means of communication ... or what's hiding in the circled letters?

Wikipedia Word definitions in Wikipedia
Backchannel is the practice of using networked computers to maintain a real-time online conversation alongside the primary group activity or live spoken remarks. The term was coined in the field of linguistics to describe listeners' behaviours during verbal ...

Wiktionary Word definitions in Wiktionary
alt. 1 To employ a back channel. 2 (context linguistics English) To employ non-verbal (oral and visual) means to influence a speaker without interruption. n. (context computing English) A real-time online discussion that occurs simultaneously with a verbal ...