Register (linguistics)

form of language used for a particular purpose or in a particular communicative situation

A register, in linguistics, is the way people use different words, spelling or grammar—talk or write differently—to different people, in different situations. They might be more polite to strangers, for example. Or they will be more respectful to their boss at work.

Formality scale
Very formal ← FORMAL      Normal      INFORMAL → Very informal
This diagram is from Quirk et al. (1985), who use the term attitude rather than style or register.

This chart shows the words or phrases that one would use depending on different registers:

Register Phrase
Very informal "Ey!" or "Yo!" or "Wassup!"
Informal "Hey!" or "Hi!"
Formal "Hello!"
Very formal "Good morning/afternoon/evening!"
change