Interrupts are used to inform the processor about occurrence of an external event. The external events could be Key presses, reception of the character on the serial port etc.
After receiving an interrupt processor stops the current task, jumps to the interrupt handler, perform required operation (detect which key is pressed or read the received character) and come back to where it was stopped by the interrupt.
interrupt in computer syatems is a mechanism wich when an event occur (like presing switch, end of adc convetion,peripheral device send an data to cpu ,etc) cpu understand and make approprite decisin .so no need cpu pooling peripheral device alternately and after reciving interrupt cpu execute predefind program for this device.
in general with interrupt we cat write more flexible programs.