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 NetscapeNavigator and Microsoft InternetExplorer now support PNG

PNG is an Acronym

InternetExplorer doesn't support alpha channels. Rumours include that the IE engine is pretty old an out of date and can't support it without lots of hidious hacks. Amusingly, while Microsoft can't make these hidious hacks, we can. Here's a site that explains how to properly render PNG's in IE with alpha transparency: http://redvip.homelinux.net/varios/explorer-png-en.html