Common parlance

Everyday language, everyday speech, common parlance, informal language, colloquial language, general parlance, or vernacular (but this has other meanings too), is the most used variety of a language, which is usually employed in conversation or other communication in informal situations.

An example of such language is called a colloquialism, or casualism. The most common term used by dictionaries to label such an expression is colloquial. Many people however misunderstand this label and confuse it with the word local because it sounds somewhat similar and because informal expressions are often only used in certain regions. (But a regionalism is not the same thing as a colloquialism, and a regionalism can be local formal speech). Much of the misunderstanding is ironically caused by the dictionary label itself being formal and not part of everyday speech. As a result, there is widespread confusion between colloquialisms and regionalisms and idioms even among dictionary users and perhaps especially among them. In addition to the problematic colloquial, Wiktionary also uses the universally understood label informal but doesn't define any difference between them.

The word colloquial by its etymology originally referred to speech as distinguished from writing, but colloquial register is fundamentally about the degree of informality or casualness rather than the medium, and some usage commentators thus prefer the term casualism.

General parlance is distinct from formal speech or formal writing. It is the variety of language that speakers typically use when they are relaxed and not especially self-conscious. An expression is labeled colloq. for "colloquial" in dictionaries when a different expression is more common in informal speech, but this does not mean that the expression is inappropriate in formal speech or writing or that it is necessarily slang. Many people misunderstand this very common dictionary label due to the widespread misconception that colloquial means "location" or a word being "regional". This is not the case; the word root for colloquial is related to locution, not location.

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Wikipedia