What main difference between UPS and inverter?

The difference between UPS and inverter is the timing that it takes for the power to kick in incase of power failure where as UPS is pretty instant inverters can take a period of 3-10 seconds 

The main difference between UPS and inverter is resume timing. UPS take less than 1 second to give power to appliances when power is failure so only its name is UPS (Uninterrupted Power Supply) but inverter which converts dc to ac takes 1 to 3 seconds to give backup to appliances.