We use the single-phase power system more 
widely than three phase system for household purposes, commercial purposes plus some extent in industrial uses. Because, the single-phase system is more economical than a three-phase system and the power requirement in most of the houses, shops, offices are little, which can be quickly met by a single phase system.
The single phase AC motors are further classified as:
Solitary phase speed reducer induction motors or asynchronous motors.
One phase synchronous motors.
Commutator motors.
The squirrel cage rotor contains aluminum, brass or copper bars. These aluminum or copper bars are called rotor conductors and placed in the slot machines on the periphery of the rotor. The copper or light weight aluminum rings permanently brief the rotor conductors called the end rings.
To provide mechanical strength, these rotor conductors are braced to the end ring and therefore form a complete closed circuit resembling a cage and hence got its name as squirrel cage induction engine. As end rings permanently short the bars, the rotor electrical resistance is very small in fact it is not feasible to add external resistance as the pubs get completely shorted. The absence of slip band and brushes make the construction of single stage induction motor very simple and robust.