PNG stands for Portable Network Graphic
This format was designed as an alternative to the GIF format because there are lingering legal problems with GIFs. CompuServe owns the format, and Unisys owns the compression method. In addition, GIF is a very basic graphics format that is limited to 256 colors (8-bit color).
Like GIF's, PNG files are lossless, meaning they don't lose any detail when they are compressed. They support up to 48-bit color or 16-bit grayscale and typically compress about 5% to 25% better than GIF files.
Like GIF's they also support transparency - and combined with the higher color depth - they are an extremely versatile image format. It should be remembered that decompressing image files takes processor time. Not an issue on the desktop - but may be an issue in mobile applications.