Graphical User Interface (GUI pronounced "gooey") enables a user to interact with a software application through graphics instead of text. The runtime (client) of Ignition is sometimes referred to as the GUI.

In scripting, "The GUI Thread" is referring to the processing power being used to draw the tables, buttons, displays, and everything else on a client. By default most event scripting is run here, but for special tasks there are ways to move the heavy work to a different area.