An OCG stands for Organized Crime Group, which is a group of people working together on a continual basis to plan and coordinate criminal behavior and conduct. OCGs are involved in various illegal activities such as racketeering, fraud, tax evasion, money laundering, arson, robbery, murder, violence, bombings, torture, health insurance fraud, human trafficking, prostitution, drug trafficking, smuggling, white-collar crimes, and both political and judicial corruption or any other illegal activity where they can make a profit. The Serious Crime Act 2015 defines an OCG as "three or more persons who act (or agree to act) together to further the carrying on of criminal activities".

Participating in an OCG is a criminal offense under section 45 of the Serious Crime Act 2015. This offense is triable on indictment only and subject to a maximum penalty of 5 years imprisonment, a fine, or both. A prosecution under section 45 may be particularly appropriate where it is possible to demonstrate that an individual has assisted the criminal activities of an OCG, but the specific nature of the underlying criminality cannot be, or is particularly challenging, to demonstrate. It is not necessary for the individual participating in the OCGs criminal activities to know any of the group members.