Too much voltage for a short period of time is a spike. Too much voltage for a long period of time is a surge. Not enough voltage for a short period of time is a sag or dip Not enough voltage for a long period of time is brownout A short power interruption is a fault A long power interruption is a blackout You MUST know all of the power issues above for the purpose of the exam.
From: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, 3rd. Edition McGraw-Hill/Osborne, 2005, page 368.