The Event Structure in LabVIEW executes code in response to a software interrupt.
The most common use-case is to respond to user interaction with a user-interface through typical input (keyboard, mouse, touch), but it can also be used to respond to events that are programmatically generated elsewhere in the software.
One event structure can be registered to respond to multiple events. Each event can execute a unique frame of the structure. A single frame can be registered to handle multiple events.
There are best-practices when using an Event Structure related to when/how it blocks and when the data flow 'reads' the user-interface element that generated the event.