In WordPress, a theme is a collection of templates and stylesheets used to define the appearance and display of a WordPress powered website.

They can be changed, managed, and added from the WordPress admin area under Appearance » Themes. There are several free and paid WordPress Themes available. WordPress.org has a large collection of free ones in their Themes Directory.

Each one comes with a different design, layout, and features. A user needs to choose the one that suits their taste and requirements for their website. There are those that are designed to serve specific kind of websites, e.g. WordPress Photography Themes are designed for photographers and photography websites.

They can be modified by adding plugins or by adding code to the functions.php file. Changes can also be made in the form of a child theme. Themes generally consists of three parts in addition to images and JavaScript files. The three parts are the style.css file, the WordPress template files, and an optional functions.php file that will allow changes to be made to the theme. Every theme must have a unique style.css file. This doesn’t mean that the styles can’t be the same but rather that the identifying information in the header needs to be different otherwise you will have problems during installation. If it is not a child theme, then it also needs to have at least an index.php template file to control the display of content.