D. Folkways
Norms for routine or casual interactions that are not strictly enforced are called "folkways." Folkways are the customary behaviors and conventions that guide everyday social interactions in a society. While they are important for maintaining social order and cohesion, they are less serious than mores, which are norms that carry a strong moral significance and are more strictly enforced. Values are general beliefs and principles that guide behavior, while mores are specific norms related to moral conduct. In this case, the description best fits the concept of folkways.