i have never seen this word before this… and interestingly a search on google just returns three websites and one of it is again dictionary.com
Dictionary.com/Word of the Day: mores

mores \MOR-ayz; -eez\, plural noun:
1. The fixed customs of a particular group that are morally binding upon all members of the group.
2. Moral attitudes.
3. Customs; habits; ways.

this is from wikipedia…
The term mores (IPA [ˈmɔːreɪz]) as used in sociology is a plural noun. The Latin singular, which is not used in English, is mos. The English word morality comes from the same root, as does the noun moral, which can mean the ‘core meaning of a story’.

Mores are strongly held norms or customs. These derive from the established practices of a society rather than its written laws. Taboos form the subset of mores that forbid a society’s most outrageous behaviours, such as incest and murder in many societies. Usually these are formalized in some kind of moral code, e.g. commandments. Most sociologists reject the thesis that the formalization matters as much as the informal social response of disgust and isolation of offenders.

However, constant exposure to social mores is thought by some to lead to development of an individual moral core, which is pre-rational and consists of a set of inhibitions that cannot be easily characterized except as potential inhibitions against taking opportunities that the family or society does not consider desirable. These in turn cannot be easily separated from individual opinions or fears of getting caught.