"Cmd + Q" is a keyboard shortcut used on Mac computers to quit an application. When you press these keys simultaneously, the currently active program will close completely, removing it from the screen and freeing up system resources. This is particularly useful for managing multiple applications and improving overall performance. Using "Cmd + Q" is different from "Cmd + W," which only closes the current window but keeps the application running. It's important to save your work before using "Cmd + Q," as any unsaved changes may be lost when the application quits.