In the early days of computing (specifically Windows 95), this area was strictly a "system tray" meant for hardware indicators like volume, network status, and clock.
On a Mac, this area is called the Menu Bar extras . These icons sit at the top right of your screen next to the Spotlight search and Siri icons.
Tray icons serve three core purposes:
They provide continuous, real-time feedback about system or application states. Examples include: