What is a .jpg file?

JPG is the most widely used image format in the world — a lossy compressed photo format that trades a tiny amount of quality for dramatically smaller files. You've been looking at JPGs your entire life. You just didn't know it. Every photo on every social media feed, every product image on every shopping site, every picture your phone has ever texted — odds are, it was a JPG. The format works by discarding visual information the human eye is unlikely to notice. That's lossy compression: the file gets dramatically smaller, and you almost never see the difference. The tradeoff is that each time you re-save a JPG, it loses a little more. JPEG was standardised in 1992 and has outlasted every format that tried to replace it. It doesn't support transparency — use PNG for that — but for photographs, nothing else comes close to its combination of quality, size, and universal compatibility.