At its most basic, a multi-outlet unit that expands the number of AC-powered devices that can be connected to a single wall outlet. Most power strips have an on/off switch for turning the power to connected devices on or off simultaneously. Various features may be added, such as a built-in fuse/circuit breaker, surge protection, line filtering, remote control master on/off switching, and more. A few power strips are even built-into rackmountable enclosures for conveniently powering up multiple units in a rack.
Most power strips are arranged with their outlets in a straight line, with the outlets quite close together. Some feature other outlet arrangements, and some allow extra space between their outlets so that wall-wart power supplies can be used without taking up two outlet spaces.
Trivia: The invention of the power strip is credited to engineer Peter Talbot, in 1972, who worked for the Kambrook company in Australia. The invention was not patented, and the company is said to have lost many millions of dollars in royalties alone from this oversight.