PNG stands for Portable Network Graphics. It is a bitmapped image format that uses lossless data compression. PNG file format does not require a patent license. PNG was designed for transfering images on the internet and not for professional graphics. The file format uses the extension .png. You can compare it to .jpg or .gif. If you switched from Windows to Linux you will notice a lot of .png files. These are just image files in the PNG format. If you would like to know more in depth information just visit the wikipedia site.