Русско-англо-русский юридический словарь

Collusion is not a crime, but colluding can be. In the colloquial sense, collusion simply means an act of secret cooperation, generally for nefarious ends. There’s no law you can violate that constitutes collusion in the third degree — but working with someone in a conspiracy to break the law is illegal.

It’s called conspiracy.

“Every conspiracy is a form of collusion,” Stanford law professor Robert Weisberg said when we spoke by phone on Tuesday. “Conspiracy is an agreement to do a crime plus some overt act in that direction. It’s really that simple.” (The Washington Post)

In criminal law, a conspiracy is an agreement between two or more persons to commit a crime at some time in the future.[1] Criminal law in some countries or for some conspiracies may require that at least one overt act be undertaken in furtherance of that agreement, to constitute an offense. (Wikipedia)