Idiosyncrasies, which comes from a Greek word which means "particular temperament", is a term associated with the character and characteristics to an individual or a community.
Although it is a subject identifiers, the idiosyncrasy contains questions that are considered from the subjective point of view. About the idiosyncrasies of a social group, may submit to the stereotype because people are not all the same characteristics. It is therefore the common characteristics shared by a large number of members in a community.
For example: the idiosyncrasies of the French includes their habit of eating croissants for breakfast, make pranks on April 1st, ("poisson d'avril"), from the weekend to the countryside to escape from big cities, to go skiing during the winter holidays, play at third (horse racing) and kiss each other with three kisses on the cheek (except in the case of men).
It cannot mean that all French eat croissants at breakfast. It's just a cultural characteristic but which is not exclusive to them. In other words, a French who dislikes all croissants isn't to much "less French' that eats several per day.
Furthermore, it y of people who kiss with two or four kisses on the cheek (depending on the region) even if it is not really the idiosyncrasy of the country.
The idiosyncrasy is noticeable from the social behaviour of people, their tastes and their professional performance. It is said, for example, that Latin peoples tend to be warmer and friendlier than Germanic or Anglo-Saxon communities. This peculiarity of the idiosyncrasy is rather noticed by people who travel everywhere in the world, and who are therefore able to compare social relations that are established in each country.