9V refers to the most common voltage used by guitar pedals for their power supply. Most standard pedals, such as overdrive, distortion, delay, and reverb, are designed to operate at 9V, which is typically supplied via a 9V battery or a 9V power adapter. This voltage is ideal for most pedals as it provides a good balance between sound quality, longevity, and ease of use.

Pedals powered by 9V are widely available and offer a broad range of effects for guitarists and bassists. The 9V supply allows for easy integration into pedalboards and works well with power strips and multi-pedal power supplies. While 9V pedals are the most common, higher voltages like 18V are also used in some high-end pedals to provide additional headroom and clarity, but for many musicians, 9V pedals offer sufficient power and performance for everyday use.