Mouse DPI for free ibp mouse (model number: MOU-IBP-003)

Its a measurement of how much the mouse responds to movement. Ie, how much the mouse moves on the screen compared to how much you move the mouse.
This is just the hardware sensitivity basically, as you can adjust the software sensitivity on the computer.

http://www.howtogeek.com/182702/mouse-dpi-and-polling-rates-explained-do-they-matter-for-gaming/
 

I know what it is...... I want to know the 3 (pretty hidden) dpi selections