Short for Portable Network Graphics, and pronounced ping, a new bit-mapped graphics format similar to GIF. In fact, PNG was approved as a standard by the World Wide Web consortium to replace GIF because GIF uses a patented data compression algorithm called LZW. In contrast, PNG is completely patent- and license-free. The most recent versions of Netscape Navigator and Microsoft Internet Explorernow support PNG.
Also see JPG vs. GIF vs. PNG in the Did You Know . . . ?section of Webopedia.