Language is the spoken or written means by which humans expresses themselves and communicate with others. The word "language" comes from the Latin lingua ("tongue"), demonstrating that speech is the primary form of language and writing the secondary. Language comprises a set of sounds that symbolize the content of the message to be conveyed. It is, on this planet, peculiar to man, consisting as it does a formal system with rules whereby complex messages can be built up out of single components. Languages are the products of their cultures, arising from the cooperative effort required by societies. There are some 3,000 different languages spoken today, added to which there are many more regional dialects. Languages may be classified into families, groups, and subgroups. To us the most important language family is the Indo-European, to which many Asian and European languages (including English) belong. Other important families are the Hamito-Semitic, Altaic, Sino-Tibetan, Austro-Asiatic, and Dravidian, among others.