Informal vocabulary is used in ones immediate circle: family, relatives or friends.
Informal style is relaxed, free-and-easy, and familiar. The choice of words is determined in each particular case not only by an informal or formal situation, but also by the speakers educational and cultural background, age group, and his occupational and regional characteristics. Informal words and word-groups are traditionally divided into three types: colloquial, slang and dialect words and word-groups. Among other informal words, colloquialisms are used by everybody, and their sphere of communication is comparatively wide, at least of literary colloquial words. These are informal words that are used in everyday conversational speech both by cultivated and uneducated people of all age groups. Vast use of informal words is one of the prominent features of 20th century English and American literature. In modern fiction informal words are not restricted to conversation in their use, but frequently appear in descriptive passages as well.
Formal style formal style is restricted to formal situations. In general, formal words fall into two main groups: words associated with professional communication and a less exclusive group of so-called learned words.
Poetic words have a further characteristic a lofty, high-flown, sometimes archaic, colouring.
Obsolete words have already gone out of use but they are still recognized by the English speakers. Archaic proper are words which are no longer recognizable in modern English.
Historisms are words used to be replaced by modern synonyms. These words are moribund, already partly or fully out of circulation, rejected by the living language. Their last refuge is in historical novels whose authors use them to create a particular period atmosphere and, of course, in poetry which is rather conservative in its choice of words.
Professional terminology. Thousands of words belong to special scientific, professional or trade terminological systems and are not used or even understood by people outside the particular speciality. Every field of modern activity has its specialised vocabulary. There is a special medical vocabulary, and similarly special terminologies for psychology, botany, music, linguistics, teaching methods and many others.
Terms. One of the most characteristic features of a term is its direct relevance to the system used in a particular science. Term is directly connected with the concept it denotes. Unlike other words it directs the mind to the essential quality of the thing. Terms are mostly used in special way dealing with the notion of some brunch of science. When a term appears in a not scientific work its function changes. In most cases it acquires a stylistic function and becomes a SD. With the increase of general education many words that were terms have gradually lost their qualities as terms. In stylistics this process is called determinisation.
