Short for JPEG File Interchange Format. When the JPEG standards committee was developing the JPEG standard, they defined the standard for representing the data in terms of its structure in memory, in terms of compression and decompression algorithms; but they got involved in a huge standards turf war over the actual JPEG file format. As a result, there is no official JPEG file format. However JFIF has become the de facto JPEG file format, even though there is no formal specification for it agreed upon by the JPEG standards committee. This has caused problems in the last few years, since the introduction of progressive JPEG images (progressive images allow a rough quality version of the image to appear, which slowly refines as more of the image data is read. With JPEG, it's not too difficult to do, you just reorder the parameters in the file) . There are other JPEG formats (like TIFF-JPEG), but they are now rare.