JPEG itself is not a file format, but rather an image compression algorithm developed by the Joint Photographic Experts Group in 1990.
The original specification did not describe a file format for data exchange. However, the Independent JPEG Group and C-Cube Microsystems developed a JPEG File Interchange Format (JFIF) in 1992, which has become a de facto standard; this is what is commonly referred to as the JPEG file format. In 1996, Part 3 of the JPEG standard was released, containing the specification for an official file format, called SPIFF (Still Picture Interchange File Format). This is more complex than JFIF, and it also supports other compression schemes.