PWM (Pulse Width Modulation)

Digital signal technique that simulates analog output by varying the duty cycle — the fraction of time the signal is HIGH.

Signal is always HIGH (3.3V) or LOW (0V) — never in between
Duty cycle = (time HIGH / period) × 100%
0% = always off, 50% = half, 100% = always on

Applications:

LED dimming: rapid switching tricks the eye
Servo motors: pulse width determines arm position

from gpiozero import PWMLED, Servo
led = PWMLED(17)
led.value = 0.5   # 50% brightness
 
servo = Servo(17)
servo.min()  # minimum position
servo.max()  # maximum position

See Also

Serial Protocols topic
GPIO and reTerminal topic