The term "JPEG" is an acronym for the Joint Photographic Experts Group, which created the standard.
.jpeg
and .jpg
files are identical.
JPEG images are identified with 6 different standard file name extensions:
.jpg
.jpeg
.jpe
.jif
.jfif
.jfi
The jpg
was used in Microsoft Operating Systems when they only supported 3 chars-extensions.
The JPEG File Interchange Format (JFIF - last three extensions in my list) is an image file format standard for exchanging JPEG encoded files compliant with the JPEG Interchange Format (JIF) standard, solving some of JIF's limitations in regard. Image data in JFIF files is compressed using the techniques in the JPEG standard, hence JFIF is sometimes referred to as "JPEG/JFIF".