To be clear, collusion is literally just concerted activity. It can be made to sound sinister, but it is not necessarily good or bad, criminal or innocent. It’s just people doing stuff together.
A subset of collusion is conspiracy. Conspiracy is a crime. Technically, it is an agreement between two or more people to commit a crime — the conspiratorial agreement is a crime even if its criminal objective is never realized.
The rationale for what the Justice Department and FBI have referred to as Trump campaign “coordination” with Russia has always been suspicion (without much proof) of a very specific kind of conspiracy: the aforementioned conspiracy to commit cyber-espionage for the purpose of influencing the 2016 election
https://www.nationalreview.com/corner/andrew-mccarthy-collusion-comments-fox-news-clarification/