A reverb pedal is a foundation guitar effects pedal for the majority of guitarists. It has the ability to thicken, include color and character to your signal. With the volume, mix, decay, pre-delay and tone controls obvious on a lot of reverb pedals under $100 you have the ability to adjust your reverb effect to precisely how you desire it.
https://www.bestguitarequipment.com/reviews/best-reverb-pedals-under-100/