Every component is a class derived from TComponent, from one of its more specialized descendants (such as TControl or TGraphicControl), or from an existing component class. The section Creating components describes which class to derive different kinds of components from. 

Deriving classes is explained in more detail in The section Defining new classes. 

To derive a component, add an object type declaration to the interface part of the unit that will contain the component. 

A simple component class is a nonvisual component descended directly from TComponent.