The macOS Dock, this operating system's version of a taskbar or Start bar, will sometimes bounce icons on it to indicate that something is happening or has happened within the application. This could range from it alerting you to an app that has finished loading, a program that has crashed, or that you received a message. However, it can be quite irritating in the midst of work, or even while watching something on your Mac. To do this, you'll need to head into the Dock & Menu Bar settings — it's called Desktop & Dock on more recent versions of macOS — within the Settings app. You can access this by opening up your Settings app and navigating to the location with the search function.