What main difference between UPS and inverter?

UPS- STANDS FOR UNINTERRUPTED POWER SUPPLY - IT PROVIDES CONTINIOUS POWER SUPPLY EVEN THERE IS A POWER CUT

INVERTER IS A DEVICE USED TO CONVERT DC TO AC POWER

UPS uninterrupture power suply 

Inverter to to convert DC to AC

Inverter: frecuency Variable.

UPS= Battery Bank for Emergency.

UPS is a system that uses an inverter. The UPS just converts AC voltage to DC  voltage then back to AC voltage again with connecting batteries in the middle process. The benefit of the UPS is incase of utility loss the system will be powered by the batteries. 

Inverter converter DC voltage to AC Voltage.