Online Media

PNG stands for Portable Network Graphics and are displayed like this

Fig 1. Google's logo

JPG stands for Joint Photographic Experts Group and are displayed like this

Fig 2. Microsoft's logo

GIF stands for Graphics Interchange Format and are displayed like this

MP3 stands for MPEG-1 Audio Layer 3 and are displayed like this

Videos are formatted using MP4, MOV, AVI, WMV, and are displayed like this

These few types of media cover a lot of what you will see on the internet.
There are many more that cover other types of media, but these are the main ones for each type.

A look into how different types of media are displayed