C# - Common Homonyms And Synonyms Between Different Webplatforms/webproducts?

I am ASP.NET developer. Yesterday I started to write website content on and support customers of plugin(s) (for example, captchas, etc.) supporting different web CMSes (Content Management Systems) on different platforms mainly PHP-based ones (like WordPress, Joomla, Drupal, etc.) though they can be for any (non-PHP) CMS (like DotNetNuke). I am trying to reuse my knowledge of ASP.NET web (user and/or server) controls, CMS DotNetNuke (dotnetnuke.com) modules, styles, CSS, master page, template, etc.

What are the differences between definitions of PHP web CMS (though it could have been written in a different language, like Python, etc.) plugin vs. MS Add-in, ASP.NET webcontrol? What are possible homonyms and synonyms a web developer/supporter between different web platforms, CMS-es, frameworks a (web)developer/supporter should be aware of? Update:@Rafe Kettler, honestly, after 2 days of writing web content for a (PHP, Python) plugin (captcha), I could not get what are its differences against asp.net webcontrol.
Why are they called differently?

There are more terms I have difficulties with between CMS-es. Note that I should communicate with both internal and external (of customers) developers developing or deploying the same plugin (product) in different platforms, languages, CMS. Update2:I do not pretend having the same instructions for different CMS-es.Instructions are specific per each CMS, but marketing (website content) should be in the same. better most common and less confusing, terms. Honestly, I am not going to study PHP and CMS-es in all possible languages (frameworks), specific responses and content will be written by developers. I am after marketing terms of a "plugin" common and unambiguous between CMS-es.