GIF (Graphics Interchange Format) is a type of image format employed by websites.
GIF possesses features that, in certain situations, make it a more flexible choice than the JPEG or PNG format. Clear GIFs are most frequently used as web beacons due to their invisibility and small file size.
GIF (Graphics Interchange Format) is a type of picture file used on the internet. It has certain special characteristics which make it more useful than JPEG or other picture file formats in certain situations.
Clear GIFs are commonly used as web beacons because they are invisible and very small so they don't affect the download speed of a webpage or email. However any sort of file could be used as a web beacon.