Acronym for Joint Photographic Experts Group.
A set of image FileFormats well suited for natural images. Standard JPEG uses lossy compression (Discrete Cosine Transform and quantisation) to significantly reduce file size while maintaining an acceptable image quality. JBIG is a specialization of JPEG for bi-level images (ie black and white). JPEG2000 is a newer, better format using wavelet compression -- which is Patent encumbered, so you're unlikely to see it implemented in OpenSource software.