"Two or more people speaking privately, with intent for the talk to remain private, around the topic of performing an immoral or inappropriate action" -Conspiracy.

It's a mundane term, and should be considered a mundane, if immoral, term. Conspiracies on lower levels happen on the daily. Conspiracy to skip out on work by calling in sick when you aren't actually, conspiracy to not tell a significant other about an affair. MOST conspiracies are simple facts of two people trying to hide a very minor wrongdoing. It's the "major" conspiracies that are the important ones.

And they need no theorizing. They're conspiracy facts.