TIF is short for Tagged Image File Format. Just as PSD it is a favoured format for the exchange of files in publishing and printing industries due to its high resolution and lossless quality. Besides, it supports the CMYK four-colour printing.
Image data are filed in strips and tiles, separately from each other. Thus, single image data can be accessed individually and loaded quickly.
The downside of its high high quality is the required memory. In contrast to a compressed JPG-image, TIF files need a multiple of the required storage space.