Circuit to generate a signal at a specific time after a trigger event. The timing can be defined by an RC time constant, or by clock pulses from an oscillator.
One way to implement a timer is as a digital counter incremented on a fixed clock frequency, allowing for generation of periodic or non-periodic timed events. It is one of the most basic and common internal peripherals found on micro-controllers, and can be used for a wide range of tasks like interrupt generation, time measurement, PWM generation, etc.