.jpg file type extension or JPEG - "Joint Photographic Experts Group" - is one of several digital image formats that are viewable in web browsers. JPEG image files are encoded using a standard for file compression (making the files smaller) that preserves essential color and display information in a fairly photorealistic way, with smooth edges, shapes and color blends. JPEG files are generally preferred for displaying still image photographs in digital form. The JPEG format is "lossy", meaning some information is lost when an image is compressed. This accounts for the "fuzziness" and patchy color areas what you may see when lower resolution JPEG images are enlarged to fill a space on the screen.
Source: U.S. Patent and Trademark Office.