A theme is a package of a set of files and settings that determine the overall look, design and sometimes functionality of a website or application. Themes define the colors, fonts, layout and other design elements of the user interface of the website or application. Themes are commonly used in website building tools, especially content management systems (CMS). For example, in a CMS like WordPress, a theme allows you to quickly and easily change the aesthetic appearance and sometimes extra functionality of the website. Themes allow users to customize their websites and achieve professional looks without the need for technical knowledge.