OSHA requires employers to protect employees from electrical hazards, including arc flash. Yet OSHA does not specifically explain how to comply with these regulations. NFPA 70E is the bridge between OSHA regulations and compliance. It is the consensus standard for electrical safety in the workplace, deferred to by OSHA on numerous occasions.
The following definitions are from the 2012 Edition NFPA 70E Standard for Electrical Safety in the Workplace.