The term 'gravelly sound' can be described as a raspy sound, which is a sound that is rough and harsh. It is often associated with a person's voice when they are speaking in a low, gruff tone. It can also be used to describe the sound of certain instruments, such as a guitar or saxophone, when they are played with a lot of distortion. The term 'RASP' is a four-letter word that is used to describe this type of sound.