This page is always accessible at: http://paratext.org/usfm
In general terms, a markup language is a special notation for identifying the components and structure of an electronic document. It combines extra information about the text together with the text itself. The extra information is what is expressed using markup. Markup can also include information about the intended presentation of the text, or instructions for how a software process should handle the text. A good markup system is easily identified as separate from the text itself.
Standard Format Markers have been used for many years within the Bible translation community as a method for identifying the unique textual elements which exist within an electronic scripture document. SFMs start with a backslash character "\" and end with the next space. Over time many different local "standards" for SFM use were developed, adapted, and used, for supporting the varied requirements of Bible translation and publishing projects around the globe.