Today JPEG is very popular as a data format. But it is not really a data format. It is an compression method. There are many compression method and JPEG is one of them. It becomes a standard in 1992 and JPEG stands for Joint Photographic Experts Group. JPEG is a lossy compression method.
Lossy compression vs Lossless compression
Lossy compression is when the compression happens it losses data and it never cannot be remade to the original image.