What an iPhone saves photos as. It isn't really an image format so much as a container holding HEVC video frames - the same codec used for film, applied to one still. That gets a photo to about half the size of the equivalent JPG, and it's also why so little else opens one: HEVC is patent-licensed, so most browsers and a lot of desktop software can't read a HEIC at all. Big photos are usually stored cut into tiles that have to be reassembled.

Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a HEIC file above and choose afterwards.