What is an interrupt in a microcontroller?

An interrupt is a signal that temporarily halts normal program execution to handle an urgent event. When an interrupt occurs, the processor saves current state (program counter, registers) to stack, jumps to Interrupt Service Routine (ISR) at the interrupt vector address, executes the ISR, then returns to normal execution. Types include external (hardware pins), internal (timers, UART), and software interrupts. Interrupts enable responsive real-time operation without constant polling, crucial for embedded systems.