The word "mellow" is an adjective that describes a state or feeling of calmness, relaxation and gentle emotions. When something or someone is described as mellow, it means they are peaceful, easy-going, and without any harsh or intense qualities. It can also refer to the quality of sound being soft and smooth, like the tone produced by a mellow guitar solo. In essence, "mellow" describes an experience that is soothing and pleasant, with no sharp edges or roughness.