A style sheet is a file or form that is used in word processing and desktop publishing to define the layout style of a document. A style sheet contains the specifications of a document's layout, such as the page size, margins, fonts and font sizes. In modern word processors such as Microsoft Word, a style sheet is known as a template. The most well-known form of style sheet is the Cascading Style Sheet (CSS), which is used for styling Web pages.
Techopedia explains Style Sheet
The term style sheet was originally used in the print publishing industry as a basis or template for creating media. It was basically a sample sheet that showed how news and magazine articles would be laid out on a page. This was carried over to desktop and online publishing software where the style sheet functions very much in the same way, except that, this time, instead of a visual guide, it affects the actual document automatically.
In digital desktop publishing and digital media, the style sheet is an abstraction and acts as a tool for separating presentation and content so that the person creating the content does not have to worry about its presentation, if the latter is done by a different person. This means that an expert on visual presentation can work on the style sheet and another expert on content creation can work on his/her side without worrying about how the content looks. This is a common feature of desktop publishing software like Adobe InDesign, PageMaker, etc., as well as of word processing software like Microsoft Word.
Some formatting elements provided by style sheets include: