JPG (or JPEG) is a file format (extension) for images which allows for compression of the file size.
The amount of compression can be adjusted to achieve a desired tradeoff between high quality and large file size - vs - low quality and small file size.
The jpg image coding standard also allows:
- An ICC profile to be embedded in the file
- Exif information to be coded into the file
The name "JPEG" stands for Joint Photographic Experts Group, the name of the committee that created the standard