A custom is a usual way to act that arises from the repetition of the same acts or by tradition. It is, therefore, habits and mores. Examples: "the customs of this people are strange to us: shops and stores closed the afternoon and reopen at dawn", "my grandfather has the custom of drinking tea before going to bed", "go to the pub after work is part of the British customs that are lost.
The custom is a social practice with roots in most of the members of a community. It is possible to distinguish the good customs (approved by the company) and bad Customs (considered negative). In some cases, the laws are intended to change behaviours that are bad habits.
As a general rule, the laws are compatible with the customs of society. Indeed, the customs can be a source of law, if the application is prior or simultaneous to the law.
For Sociology, customs are elements of culture that are transmitted from generation to generation and which, therefore, relate to the adaptation of the individual to the social group.
There are different types of social considerations relating to customs. In France, for example, serves first ladies and men and it is polite to finish the food that's on his plate. In China, on the other hand, it is more polite to leave a little on the plate to eat everything. Although this is not illegal in France, society will tend to criticize or censure those who do not respect the customs of the country and that act differently.