Don't know What is WordPress Theme! A theme is a collection of templates and stylesheets used to define to display of  WordPress powered website.
I know in this web development world "What is WordPress Theme?" is a funny question. But I also surprised to know 2400 plus people or web developers search monthly to know about these terms.
However, I will try to explain all the information briefly about WordPress themes and Wordpress Content Management System...
WordPress is a CMS (Content Management System). It builds with PHP and MySQL or MariaDB database servers. Now a day it is the most popular CMS in the world for a lot of features specially free custom themes. It initially released on 27 May 2013 and updated regularly. It is a free website software so anyone can use it for personal or commercial purposes.
Download WordPress CMS from WordPrss.org and install it in your server to build your own website or your client.
WordPress theme mainly a layout base on WordPress CMS. It builds with all the necessary features to present your business as a website. Themes layout depends on the business category. Almost all types of websites are able to create with WordPress template.
There are many theme marketplace are selling WordPress themes and templates to build any kind of website. Just you have to choose the right Wordpress template for your business.
According to WpBeginner:
A theme is a collection of templates and stylesheets used to define the appearance and display of WordPress powered website. They can be changed, managed, and added from theWordPress admin area under Appearance » Themes
Sometimes we find our business or blog related theme online to develop our own business website or blog site following another website. But how to know what theme is used on the website?
You can find any WordPress website theme details following 2 methods.
View the source code of the website (Ctrl + U) and find style.css file
Click on style.css file
Now find the Theme Name like the above image
You can use the WordPress theme detector to know details about a WordPress theme and plugin. Use the ScanWP tool for detailed information.
There are many free and paid themes online. You can download it from various theme directory or use it from the theme gallery Appearance>Themes of Admin Panel. Please follow the video and know the WordPress theme installation process.
I think you have watched the video carefully. If you have any questions about the theme installation process, please contact or ask us just place a comment.
You can follow our WordPress guideline to add new features to your WordPress Theme.
In this, What is WordPress Theme topic I tried to inform you about WordPress and WordPress themes? If you learn theme development and create a custom Wordpress theme, you can make money online doing freelancing and selling featured templates using large marketplace Themeforest, Template monster even using your own website.