The term Language Register was first used by Reid in 1956 and popularized by linguist in the 1960s. Also known as tenor, tone or style, it refers to a variety of language used by speakers in particular social settings.
A register is a variety of a language used in a particular social setting, using certain words, phrases and contractions that are not normally used in other settings (or if they did, they may sound strange or out of place).
Jargon is technical terminology used for a special activity or by a special group, such as computer geeks, scientists, lawyers and so on.
Martin Joos (1961) describes five styles in spoken English: frozen or static register, formal, consultative or participatory, casual and intimate.
Frozen or “static” register
At this level, language is literally ―frozen‖ in time and form. It does not change. This type of language is often learned and repeated by rote. Examples include biblical verse, prayers, the Pledge of Allegiance, and so forth.
Formal register
This style is impersonal and often follows a prescriptive format. The speaker uses complete sentences, avoid slang and may use technical or academic vocabulary. It is likely that the speaker will use fewer contractions, but opt instead for complete words. (Example: have not instead of ― haven‘t).
Consultative register
This is the register used when consulting an expert such as a doctor. The language used is more precise. The speaker is likely to address the expert by a title such as ― Doctor, ― Mr. or ― Mrs. Some sources say this register is the formal register used in conversation.
Casual register
This register is conversational in tone. It is the language used among and between friends. Words are general, rather than technical. This register may include more slang and colloquialisms.
Intimate register
The language used by lovers. It is also the language used in sexual harassment. This is the most intimate form of language. It is best avoided in public and professional situations.
Language register is the level and style of your writing. It should be appropriate for the situation you are in. The language register determines the vocabulary, structure, and some grammar in your writing.
The formal register is more appropriate for professional writing and letters to a boss or a stranger.
The informal register (also called casual or intimate) is conversational and appropriate when writing to friends and people you know very well.
The neutral register is non-emotional and sticks to facts. It is most appropriate for technical writings.
Formal writing is probably the most difficult type of writing. It is impersonal, meaning it is not written for a specific person and is written without emotion.