Client-side decoration (CSD) is the concept of allowing a graphical application software to be responsible for drawing its own window decorations, historically the responsibility of the window manager.[1]
Sometimes client-side decoration is used to refer to the applications that don't have a traditional title bar. However, this is a misuse of the phrase, as even applications that have a basic title bar can be client side decorated.[2]
By using client-side decoration rather than traditional server-side decoration, applications are able to draw their own title bar, which allows for a wide range of possibilities to customize window decorations and add additional functionality (graphical control elements) into what otherwise would be a typical window manager bar with much empty space in the maximized windows.[3]