About pages contain documentation for plugins that becomes accessible at a sites when each plugin is installed. An about page title is constructed from the plugin name surrounded by "About" and "Plugin".
Typically an about page contains a synopsis, an example, a description of markup and a link to source code for the plugin. Complex plugins may spread this information across multiple pages linked from the about page.
In rare cases a plugin will introduce an about page that does not follow title conventions. This happens when a plugin is generally useful without any customization. For example, Recent Changes.