The web platform is a description of what the web has become based on its wide-ranging usage. The web itself is now as significant and complex as many operating systems putting it into the platform category—particularly with Electron showing full desktop applications can be created with nothing but web technology.
Categories of the Web
One way to make sense of web development is to categorize the different uses for the web and therefore the technologies related to that usage:
Breaking the web down into major categories like this is particularly important for those wanting to learn or teach web technology because the web platform has so many vastly different but interrelated technologies involved.
For example, writers only need understand Markdown and the document web; software developers increasingly must keep up with all the frameworks and innovations for the application web aka the web platform; YouTube® stars, Twitch® streamers, and Netflix® film directors master audio and video content production for the broadcast web; those creating conversational content that can be queried or read with speech synthesis have yet a different approach.