Final answer:
The tilde (~) symbol next to a pin number means that the pin supports pulse width modulation (PWM), which allows for varying power levels similar to analog voltage by modulating the duty cycle of a digital signal.
Step-by-step explanation:
The tilde symbol (~) next to a pin number on a microcontroller board, such as those found on Arduino boards, indicates that the pin supports pulse width modulation (PWM). This means that the pin can be used to simulate analog voltage levels through PWM, which is a technique used to encode information on a digital signal or control the amount of power delivered to an electronic device, like an LED or a motor. PWM allows for the modulation of the duty cycle of a digital signal, where the signal is switched between on and off at a fast rate, and the proportion of the time spent in the on state is changed to adjust the power delivered. While digital signals are either in a high (on) or low (off) state, by varying the duty cycle, PWM essentially creates a signal with a variable average voltage, which resembles an analog signal's behavior.