Say "Stay on subject"
a normal conversation is a group of people talking about a subject.
If you are talking about the theme of a book, synonyms are lesson or moral. If you are talking about the theme of the conversation or meeting, synonyms are matter or subject or topic.
A guy would say so when a conversation subject finished while texting if he wants to keep talking to you. He may like you.
Are you talking about having your conversation taped by police? Basically, the rule is at least one person involved in the conversation has to know that the conversation is being recorded, otherwise there needs to be a search warrant. For example, if I were a police officer and I was talking to you, I could record the conversation without your consent or knowledge, because I am involved in the conversation, and I know it is being recorded. However, if I am a citizen talking on the phone to another citizen, a search warrent would be required because neither subject was aware of the recording being made.
'conversation'
no...you need another person to hold an conversation...and if your talking to yourself its not normal 0.0
just start talking
"What are we talking about?"
An euphemism for talking could be "communicating" or "having a conversation."
It means to start talking to someone.
Conversation
A conversation where two people are talking about different things (thinking mistakently that they are speaking of the same subject) is 'un quiproquo' (masc.) (from Latin Quid pro quo, a thing taken for another).