RCP is a platform for building rich client applications with desktop-like functionality using Java. It includes components like SWT and JFace for building the user interface, OSGi for modularity, and tools for deployment and updating. RCP allows creating applications with a native look and feel that can integrate tightly with the desktop and be deployed across platforms. It is reusable since applications are built from plugins, and existing RCP applications and libraries can be leveraged without building from scratch.