PWM stands for Pulse Width Modulation. Electronic circuits can contain both analogue and digital components. PWM allows you to control analogue devices using a digital signal. Many electrical designs use PWM for regulation.
Analogue signals can be on or off, but they can also be half-way on etc. Whereas a digital signal has just on or off positions. Both signals appear in electronic circuits and are required to work together. Inputs can be converted using a DAC or ADC. PWM is available to control the output of a device. For example, a PWM can convert the digital output of a microcontroller (MCU) into an analogue signal, to drive the next analogue component.
PWM signals feature two main things, frequency and a duty cycle. Duty cycle is given as a % and refers to the amount of time the signal is on. For example, if the duty cycle is 50%, the signal is on for 50% and off for 50% of the time period. Pulse width modulation uses a rectangular pulse wave.