You can’t watch certain videos on the web without a plugin. Plugin files are software components that add a specific features to existing software applications. You may have heard of Adobe Flash Player and QuickTime Player. These are plugins.
Plugin files can be used by applications for image, video, audio editing, and even Web browsers. Popular plugin extensions are .CRX (Google Chrome extneion), .XPT (Mozilla Firefox component), .8BI (Adobe Photoshop plugin) and .API (Adobe Acrobat plugin).