Blackout: A cutoff of electrical power, especially as a result of a shortage, a mechanical failure, or overuse by consumers.

Brownout: Common term for under voltage, taken from the coloration of filament style light bulbs during under voltage conditions.

Flicker: A small change in line voltage, which causes a perceptible change in the intensity of electric lights. In some situations people can detect sags as low as a third of a volt.

GFI (also GFCI): ground fault interrupter, or ground fault circuit interrupter, an electrical device that senses a fault in the electrical system and shuts down power to that device.

Ground: A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth or to some conducting body of relatively large extent that serves in place of the earth.

Harmonic: A harmonic is a signal or wave whose frequency is an integral (whole-number) multiple of the frequency of the main power frequency (ours is 60Hz). These can cause many problems and should be remedied as soon as detected.

Joule Ratings: This is the amount of energy a unit can dissipate before it fails -- the higher the rating the better.

Load: how much electricity or energy you use in a given period of time.

Open Circuit: a circuit having a break in it so that current is not passing or cannot pass. (generally a blown fuse)

Over-voltage: When used to describe a specific type of long-duration variation, refers to a voltage having a value of at least 10 percent above the nominal voltage for a period of time greater than 1 min.

Short Circuit: A low-resistance connection established by accident or intention between two points in an electric circuit.

Transient: A sudden, brief increase in {current} or {voltage} in a circuit that can damage sensitive components and instruments.

UL Rating: UL (Underwriters Laboratory) is a non profit organization that test electronic products for there safety.

Under-voltage: When used to describe a specific type of long-duration variation, refers to a measured voltage having a value at least 10 percent below the nominal voltage for a period of time greater than 1 min, In other contexts, such as distributed generation protection, the time frame of interest would be measured in cycles or seconds.

Voltage Sag: A decrease of 10 to 90% in the RMS voltage at the power frequency for durations of one-half cycle to 1 minute.

Voltage Swell: A temporary increase in the RMS value of voltage of more than 10% at the power frequency, for durations from one-half cycle to one minute (commonly called a surge).