When saving images from a website, you might have ended up with an image in the WebP format. Here's all the info on the WebP file format.
WebP is a lossy and lossless compression method developed by Google that can be used on a large variety of photographic, translucent, and graphical images found on the web. The degree of lossy compression is adjustable so that users can choose the trade-off between file size and image quality. WebP typically achieves 30% more compression than JPEG and JPEG 2000, without loss of image quality.
In other words, the WebP format essentially aims at creating smaller, better-looking images that can help make the web faster.
WebP images can be opened in most modern web browsers.