What is HEIC?

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.

What is WebP?

Google's format for the web, and a genuine improvement on both of the formats it replaces: lossy like JPG or lossless like PNG, transparency either way, and usually about 30% smaller. Every current browser reads it. Software that stopped being updated around 2019 often doesn't.