In short, mores "distinguish the difference between right and wrong, while folkways draw a line between right and rude".[1]
Both "mores" and "folkways" are terms coined by William Graham Sumner in 1906
folkway, the learned behaviour, shared by a social group, that provides a traditional mode of conduct. According to the American sociologist William Graham Sumner, who coined the term, folkways are social conventions that are not considered to be of moral significance by members of the group (e.g., customary behaviour for use of the telephone). The folkways of groups, like the habits of individuals, originate in the frequent repetition of acts that prove successful for satisfying basic human needs. These acts become uniform and are widely accepted. Folkways operate primarily at an unconscious level and persist because they are expedient. They tend to group themselves around major social concerns, such as sex, forming social institutions (e.g., the family). Sumner believed that folkways from diverse areas of life tended to become consistent with each other, creating definite patterns.
Tradition, habit, and religious sanctions tend to strengthen folkways as time passes, making them more and more arbitrary, positive, and compelling. Some folkways become mores (borrowed from the Latin word for customs by Sumner) when they become ethical principles, the behaviours considered essential to the welfare of the society. Mores are more coercive than folkways: relatively mild disapproval follows an infringement of a folkway; severe disapproval or punishment follows the breaking of mores. Polygamy violates the mores of American society; failure to wait one’s turn in line is a breach of folkways.
Sumner saw folkways and mores as essentially conservative and doubted the ability of members of the society to change