CakePHP is a web framework built in php. A web framework is a concept that has been developed from the understanding that most web applications - at their core are quite similar. A web frame work provides a foundation of components which web applications can be built on. With a web frame work in place and preferably out of sight - developers can devote more time to their sites core functionality.
The features within CakePHP are those that are common to nearly all web applications. By coming up with best practices to structure a web application, less time has to be spent determining the best code layout and educating new members of a team.