JFIF stands for 'JPEG File Interchange Format'.
JFIF is a minimal image file size most often used in browser thumbnails.
JFIF is also the most annoying file format ever because literally every single image sharing website rejects it.
FRIEND: Hey dude I find this hilarious meme! I'll send you it rn
OTHER FRIEND: Where is the image?
FRIEND: For some reason this site hates JFIF. I can't send it