Flash is a program tool which lets develop different interactive multimedia applications. The using of Flash is different, it may be games, web sites, CD-presentations, banners or even cartoons. Making the final product you can use media, audio and graphical files. You can also create interactive interfaces and full-fledged web-applications based on PHP and XML.
Flash player is a player for files in Flash format.
Flash-files have .swf extension and may be reproduced by Flash Player, which may be installed as the plugin to your browser.