Joint Photography Group (or Joint Photography Experts Group) is one of several file types for storing photographic images.
JPG files are lossy, meaning that image quality can decline during editing and multiple resaves.
JPG images can be saved with various levels of quality/compression. Some software describes quality on a scale of High to Low, or using a numeric system of 12 down to 1 (twelve is the highest quality with the least compression.)
Caution is advised when resaving JPG images: the compression used to reduce file size can introduce disruptive artifacts that become visible at lower resolutions or with lower-quality compression. Multiple saves tend to exaggerate these artifacts even further.
When providing JPG images for publication, it is best to provide the original image from the camera or imaging device.
Other common photo formats include TIF, PSD, and GIF. Less common formats include RAW, BMP, and PCT.