A style guide is a set of standards for the writing, formatting, and design of documents. A book-length style guide is often called a style manual or manual of style (MoS or MOS). (Typical examples include the Chicago Manual of Style and the AMA Manual of Style.) A short style guide, of several pages or several dozen pages, is often called a style sheet, although that term also has multiple other meanings. The standards documented in a style guide can be applied either for general use, or be required usage for an individual publication, a particular organization, or a specific field.
A style guide establishes standard style requirements to improve communication by ensuring consistency both within a document, and across multiple documents. Because practices vary, a style guide may set out standards to be used in areas such as punctuation, capitalization, citing sources, formatting of numbers and dates, table appearance and other areas. The style guide may require certain best practices in writing style, usage, language composition, visual composition, orthography, and typography. For academic and technical documents, a guide may also enforce the best practice in ethics (such as authorship, research ethics, and disclosure) and compliance (technical and regulatory). For translations, a style guide may be used to enforce consistent grammar choices such as tenses, formality levels in tones, and localization decisions such as units of measurements.
Style guides are specialized in a variety of ways, from the general use of a broad public audience, to a wide variety of specialized uses, such as for students and scholars of various academic disciplines, medicine, journalism, the law, government, business in general, and specific industries. The term house style refers to the styling defined by the style guide of a particular publisher or other organization.
Style guides vary widely in scope and size, and writers working in most large industries or professional sectors reference a specific style guide, written for their industry or sector when writing very specialized document types. These guides are, for the most part, only relevant and useful for peer-to-peer specialist documentation or to help writers working in specific industries and/or sectors communicate highly technical information in scholarly articles or industry white papers.
Professional reference style guides from different countries give authoritative advice on their language and how to use it, such as the New Oxford Style Manual from Oxford University Press, UK and The Chicago Manual of Style from the University of Chicago Press, US; Australia and Canada both have style guides created by their governments which are available online.
This variety in scope and length is enabled by the cascading of one style over another, in a way analogous to how styles cascade in web development and in desktop cascade over CSS styles.