JPEG and JPG are file types that refer to the same format for lossy compression of images. Computers treat either extension (".jpg" or ".jpeg") as the same type of file. JPEG stands for "Joint Photographic Experts Group," who are the developers of this file format.
JPEG is a popular image format because it can compress highly detailed images into manageable file sizes. However, the lossy side effects of compression lead to a slightly altered image compared to the raw data. This makes JPEG a convenient format for widespread sharing of images but unfit for archival purposes. The anti-aliasing present in JPEG can also lead to blurring of particularly fine lines.