Answer Description

A brownout is when voltage drops suddenly below the expected levels causing intermittent issues for electrical devices. A power surge is the opposite (increase in power) and a blackout is a total loss of power.

Wikipedia

A brownout is a drop in the magnitude of voltage in an electrical power system. Unintentional brownouts can be caused by excessive electricity demand, severe weather events, or a malfunction or error affecting electrical grid control or monitoring systems. Intentional brownouts are used for load reduction in an emergency, or to prevent a total grid power outage due to high demand. The term brownout comes from the dimming of incandescent lighting when voltage reduces. In some countries, the term brownout refers not to a drop in voltage but to an intentional or unintentional power outage (or blackout).