A style guide or manual of style is a set of standards for the writing, formatting, and design of documents. It is often called a style sheet, although that term also has multiple other meanings. The standards 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).
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 individual style manual of a particular publisher or organization.
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. The exceptions to the rule are The Associated Press Stylebook and The Chicago Manual of Style. The reason is both style guides focus on "general", third-person English. The Associated Press Stylebook is, indeed, written for journalists, and The Chicago Manual of Styleis written for academic writing. However, these two industries/sectors also make up the largest segment of professional writers for North American, third-person English. They are also edited and published by hundreds of professional writers who are focused on improving communications across the largest segment of the North American population. No other style guide can claim to follow the same level of scrutiny, review and approval. This is why writers of all types reference one of these two guides more than all other style guides combined for most documentation written within all North American industries and sectors.
Most other style guides are written for industries and sectors unrelated to writing and should only be referenced for peer-to-peer documentation. The goal of most industry style guides is to help writers working in specific industries and/or sectors communicate highly technical information in scholarly articles or industry white papers. To reach the largest audience, only The Associated Press Stylebook or The Chicago Manual of Style should be referenced. The exceptions would be when these two manuals do not provide styles (e.g. Use of The Microsoft Manual of Style to describe general software navigation and procedural steps).
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.