A widget is a GUI element: A button, a text field, ... The sample application in this directory shows the most common PyQt widgets:
If you know HTML: Widgets are a little like HTML elements. They can be nested, and have a different appearance and behavior depending on their type. (Eg. a link <a> looks and behaves differently from an image <img>.)
Some of the widgets you can see in this screenshot are:
The source code for this application is in main.py. For instructions how to run it, please see here. Don't worry if you don't yet fully understand the source code. The main purpose of this example is to give you a feel for what a widget is, and which ones are available. The next examples give you a more gradual route to more advanced PyQt topics.