A component as defined in: Class
java.awt.Component of the awt docs is: an object having a
graphical representation that can be displayed on the screen and that can
interact with the user. Examples of components are the buttons, checkboxes,
and scrollbars of a typical graphical user interface. Everything you
can see in the gui is derived component (with the exception of menu bars,
go figure).
So a checkbox is a component in the following applet: