What is an event handler?

An event handler is specifically defined as code that is executed in response to a particular event occurring within a software application. In programming, events can occur as a result of user interactions, such as clicking a button, pressing a key, or moving the mouse, as well as system-generated events like timers or data changes.

When the designated event occurs, the corresponding event handler is triggered, allowing developers to define how their program should respond to these interactions. This mechanism is fundamental in event-driven programming, ensuring that applications react dynamically to user input and other stimuli.

The other options presented represent different concepts in software development that do not align with the definition of an event handler. For example, user interface components refer to elements like buttons and text fields that users interact with, while managing database queries involves operations related to accessing or modifying data in a database. Tools for debugging are used for identifying and fixing errors in code, but they do not define event handling directly.