Discretion means the choice to do something e.g. police powers= discretion to issue fines etc., the public have discretion in reporting a crime, judges have discretion in issuing sentencing. You must link this to the key terms of the question, e.g. the fact that the public have discretion in reporting a crime can limit the justice of the criminal justice systemm as often domestic violence and sexual offences are underreported due to fear of retribution