WebP is a modern image format developed by Google. It compresses photos and graphics more efficiently than JPG and PNG, so pages load faster and files take up less space — at the same visible quality. It also supports transparency, like PNG.
The downside: some older apps and workflows still don't recognise WebP, which is why people often convert it back to JPG or PNG.
You can convert to WebP to shrink files, or convert WebP back to JPG when you need wider compatibility.