A crime scene is a location where an illegal act took place, and comprises the area from which most of the physical evidence is retrieved by trained law enforcement personnel, crime scene investigators (CSIs) or in rare circumstances, forensic scientists.
Strictly speaking, a crime scene is a location wherein evidence of a crime may be found. It is not necessarily where the crime was committed. Indeed, there are primary, secondary and often tertiary crime scenes. For instance, the police may use a warrant to search a suspect's home. Even though the suspect did not commit the crime at that location, evidence of the crime may be found there. In another instance, an offender might kidnap at one location (primary crime scene), transport the victim (the car being a secondary crime scene), commit another crime at a distant location (murder, for instance) and then dispose of the body at a fourth scene.
All locations where in there is the potential for the recovery of evidence must be handled in the same manner. They must be protected from interference of any kind so as to preserve any trace evidence. It is usually achieved by taping a wide area around the crime was committed to prevent access by any person other than the investigators. The conditions at the crime scene must be carefully recorded in great detail, as well as conserved. Only when recording has taken place can items be removed for laboratory analysis.
Legal concepts impacting the usefulness of evidence in court (Daubert, chain of custody,etc.), apply to the recovery of evidence whether or not a crime actually occurred at that location.