By referring two sources provide a definition of the concept gang

Source 1 (Merriam-Webster Dictionary):

"A gang is a group of criminals or hoodlums who associate for the purpose of committing crimes, especially involving violence or drugs."

Source 2 (Federal Bureau of Investigation):
"A gang is an organized group of criminals, often operating in multiple states and even internationally, with a hierarchical structure and defined leadership. Gangs engage in illegal activities such as drug trafficking, extortion, violence, and other criminal enterprises."

Source 1: Merriam-Webster Dictionary

According to Merriam-Webster Dictionary, a gang is "a group of criminals or hoodlums who band together for mutual protection and profit."

Source 2: Britannica Encyclopedia

As per Britannica Encyclopedia, a gang is "a group of persons, usually youths, who share a common identity and who generally engage in criminal behavior. In contrast to the criminal who operates alone or for immediate family gratification, gangs are complex organizations with defined territories and regular affiliations with one another."

To provide a definition of the concept "gang," I will refer to two sources: the Oxford English Dictionary (OED) and the U.S. Department of Justice's National Gang Center.

1. According to the Oxford English Dictionary (OED):
The OED defines a gang as "a group of young people who are regularly together and who often fight against other groups, especially in order to take control of an area, sell drugs, etc." This definition highlights the association of a gang with a group of individuals engaged in criminal activities, often involving violence or control over a particular territory. The OED also notes that the term "gang" can have broader uses, including non-criminal or nonviolent contexts.

2. According to the National Gang Center (an initiative managed by the U.S. Department of Justice):
The National Gang Center defines a gang as "a group or association of three or more persons who have a common identifying sign, symbol, or name, and whose members, individually or collectively, engage in criminal activity that creates an atmosphere of fear and intimidation." This definition focuses on the specific criteria used to identify a group as a gang, such as having a shared identifier, engaging in criminal activities, and instilling fear in the community.

By referring to these two sources, the definition of a "gang" encompasses the idea of a group of individuals frequently associated with criminal activities, typically involving violence, control over a specific territory, and creating an atmosphere of fear and intimidation.