WordPress themes are pre-designed templates that determine the look and feel of a WordPress website. They control the layout, color scheme, fonts, and overall visual appearance of a site. Themes can be easily installed and activated in the WordPress dashboard, allowing you to quickly change the appearance of your website without having to modify any code. There are thousands of free and paid WordPress themes available, ranging from simple blog-style designs to complex e-commerce themes. The choice of theme can have a significant impact on the usability, functionality and overall success of a website.