A WordPress theme is a combination of files that make up a website using the WordPress CMS. A theme often consists of different parts, such as functionalities, icons and fonts. This ultimately forms the style of a website.
WordPress allows you to manage a theme without too much knowledge. Think of adjusting texts, images, pages and the menu bars. This makes managing a website easy without having to code.
You can develop WordPress themes yourself, but can also be purchased for a few euros through various websites. These (paid) themes have been developed to provide companies, blogs and hobbyists with a professional website quickly and cheaply.