A typical UI will be composed of many widgets, and some of them will never change their properties after being instantiated. They do not have a state; that is, they do not change by themselves through some internal action or behavior. Instead, they are changed by external events on parent widgets in the widgets tree. So, it's safe to say that stateless widgets give control of how they are built to some parent widget in the tree. The following is a representation of a stateless widget:

So, the child widget will receive its description from the parent widget and will not change it by itself. In terms of code, this means that stateless widgets have only final properties defined during construction, and that's the only thing that needs to be built on the device screen.