Emacs: What do `mouse-1`, `mouse-2` buttons etc. mean?

Where are the following buttons located on my mouse?

EDIT: I have added locations in brackets after answer by Jack.

• mouse-1 (Left button)
• mouse-2 (Wheel button click / Middle button)
• mouse-3 (Right button)
• mouse-4 (Wheel up)
• mouse-5 (Wheel down)