Racial profiling refers to the use of an individual’s race or ethnicity by law enforcement personnel as a key factor in deciding whether to engage in enforcement (e.g. make a traffic stop or arrest). The practice is controversial and is illegal in some nations.
The concept of racial profiling has been defined in many ways, including:

• "Any police-initiated action that relies on the race, ethnicity, or national origin rather than the behavior of an individual or information that leads the police to a particular individual who has been identified as being, or having been, engaged in criminal activity." -Deborah Ramirez, Jack McDevitt, Amy Farrell for US DoJ
  United States Department of Justice
  The United States Department of Justice , is the United States federal executive department responsible for the enforcement of the law and administration of justice, equivalent to the justice or interior ministries of other countries.The Department is led by the Attorney General, who is nominated...
  
  

• "Racially-biased policing occurs when law enforcement inappropriately considers race or ethnicity in deciding with whom and how to intervene in an enforcement capacity."_{-Lorie Fridell, Robert Lunney, Drew Diamond and Bruce Kubu}

• "Using race as a key factor in deciding whether to make a traffic stop." _{-General Accounting Office}

• "In the literature to date, there appear to be at least two clearly distinguishable definitions of the term 'racial profiling': a narrow definition and a broad definition...