Meaning
A trackball, a pointing device with a large ball set in a base that you roll with your fingers or thumb instead of sliding a mouse. It means moving a cursor and controlling a computer.
It is fairly rare in chat and turns up among designers, arcade fans and people with wrist strain who prefer rolling to sliding: “Switched to a 🖲️ last month and my wrist is grateful.” Some people mistake it for a joystick or a big round button.