We utilize the single-phase power system more widely than 3 phase system for domestic 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 the majority of the houses, shops, offices are small, which can be very easily met by a single phase system.
The single phase AC motors are further classified as:
Solitary phase induction motors or asynchronous motors.
Solitary phase synchronous motors.
Commutator motors.
The squirrel cage rotor includes aluminum, brass or copper bars. These light speed reducer weight aluminum or copper bars are called rotor conductors and positioned in the slot machines on the periphery of the rotor. 
The copper or light weight aluminum rings permanently short the rotor conductors known as the end rings.
To provide mechanical strength, these rotor conductors are braced to the finish ring and hence form a complete closed circuit resembling a cage and hence got its name since squirrel cage induction electric motor. As end rings completely short the bars, the rotor electrical resistance is very small and it is not possible to add external resistance as the bars get completely shorted. The absence of slip band and brushes make the construction of single stage induction motor very simple and robust.