The term 'Directional Suffix' refers to a three-letter suffix that is added to the end of a word to indicate direction. The most common directional suffix is 'ern, ' which is used to indicate a direction towards the east. This suffix is often used in geographical terms, such as 'northeast' or 'southeast.' It can also be used to indicate a direction in relation to a person's body, such as 'rightward' or 'LEFTWARD.'