In broad terms, it means a defendant engaged in a conversation or other pattern of activity in which the intent was to commit an act of racketeering.
For example, your defendant is talking to some friends who decide they want to sell drugs in the neighborhood. The group discusses how they'll go about setting up their cartel, etc. That's a conspiracy.
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Conspiracy is an "inchoate" crime, meaning not fully completed. It is the conversation to set up the crime. It is graded at the same degree as the most serious crime planned but a first degree crime is a second degree conspiracy. They must have dropped it to a third degree because a second havs a presumption of State Prison even if treated as a third.