GUI stands for Graphical User Interface, which is a user-friendly visual experience builder for Java applications. It comprises graphical units like buttons, labels, windows, etc. via which users can connect with an application. Java provides a set of user interface components from which GUI forms can be built. Swing and JavaFX are two commonly used applications to create GUIs in Java. Swing is a flexible architecture designed to make the elements customizable and easy to plug-and-play, which is why it is the first choice for Java developers while creating GUIs. JavaFX consists of a totally different set of graphic components along with new features and terminologies.

To create a GUI in Java, the process starts with creating a class that represents the main GUI. An article of this class acts as a container that holds all the other components to be displayed. The IDEs GUI Builder assists in designing and building Java forms by providing a series of tools that simplify the process. The components that comprise a GUI are stored in containers called forms.

In summary, GUI in Java refers to the visual components of a Java application that allow users to interact with it. Swing and JavaFX are two commonly used applications to create GUIs in Java. The IDEs GUI Builder assists in designing and building Java forms by providing a series of tools that simplify the process.