All the below definitions should be read in the context of web development and WordPress.
What is WordPress?
WordPress is a website builder and content management system. It is written in PHP (a scripting language that is suited for web development) alongside a MySQL or MariaDB database.
A scripting language is a computer language that is good for interpreting and communicating with other computer languages. All programming languages are just code (electrical signals) that effectively talk to computers. A database is a set of structured information stored and accessed by a computer.
The scripting language and the database are combined together to create a website. The PHP does the server-side processing and generates HTML whilst the MySQ/MariaDB is for the storage and retrieval of data. When a user comes to a site, PHP code is run on the server to generate the HTML of the page and within that process, queries are sent through and retrieved from the database.
A server is a computer or system that provides resources and data to other computers. Data centers are facilities that house servers.
Theme
A theme is collection of templates and stylesheets that define how your website looks and how users are able to interact with it. There are thousands of different themes- paid and free.
What is a template?
A pre-existing file that serves as the foundation for a web page on your site. They are used to create a consistency across the website as to how it looks and feels to the user.
Plugin
A plugin is a bit of software containing a group of functions that can be added to a site to complete a task, to add functionality to a site, to redesign a look or put in a new feature. Plugins allow you to do these things without having to completely redesign the website.
Elementor
This is a very popular page builder plugin for WordPress which allows people who don’t have coding skills to customize their website. It provides easy and wider access to web design and development.
Widget
An element that is used to add content or features, usually to the sidebar or footer of your website. A widget is a simpler, more specific tool than a plugin. A plugin is more complicated, has a wider scope; a plugin might include 1 or more widgets.