WebP

WebP is a file format developed by Google to allow for images to be stored more efficiently on the web. It supports both :.|:;y and :.|:;less encoding of images and animated images.

Advantages over other formats

WebPs often offer better image quality at similar file sizes over formats such as JPEG, and may also help reduce the storage cost of lossless media compared to PNGs.
The format supports transparency for :.|:;less images, something that still isn't widely supported by the JPEG standard.
Animated WebPs offer way better compression than gifs, along with support for 24-bit color with transparency and other goodies.

Disadvantages

There is none! ^{[citation needed]}