Unofficial means of communication

• Covert means of communication ... or what's hiding in the circled letters?
• Unofficial means of communication, and a hint to each set of circled letters

Wikipedia Word definitions in Wikipedia
In linguistics , backchannels are listener responses in a primarily one-way communication. These can be both verbal and non-verbal in nature, and are frequently phatic expressions , primarily serving a social or meta-conversational purpose, rather than ...

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 ...