Organized crime is a term typically used by police to describe a group of people collectively engaged in ongoing criminal activities. These groups can be motivated by profit or political reasons. Involvement in such a group is often regarded as a crime in and of itself.
On Earth in the 20th century, members of organized crime were sometimes referred to as gangsters. The inhabitants of Sigma Iotia II modeled their society on the organized crime from that period found in the novel Chicago Mobs of the Twenties, left behind by the starship Horizon.(TOS: "A Piece of the Action", DS9: "Badda-Bing, Badda-Bang")
The Orion Syndicate is an example of organized crime in the 24th century. They would undertake criminal activities designed to affect the politics of whoever was willing to make use of their services. During the Dominion War, they collaborated with the Dominion to assassinate a Klingon ambassador, which was set up to sow dissent within the Klingon Empire so Dominion forces could exploit it. (DS9: "Honor Among Thieves")
Organized crime does not tolerate betrayal, and will take action to prevent its members or anyone who makes contact with them from going to the authorities. Quark and Odo once survived an assassination attempt from the Orion Syndicate, when Odo took Quark to Inferna Prime to testify before a Federation Grand Jury about the Syndicate's activities. (DS9: "The Ascent")