Surfing Waves

two things. first what does a bat tail do, and second i saw this board at a restorant and all my friend and i agree that its a bat tail but the center of the tail is rounded and not a point. is it still a bat tail or is it something else?

This is a bat tail:





It is still a bat wing if it is slightly rounded instead of a point.
They are mainly used on thicker boards, usually with a quad fin setup to help in the control of the board a bit like a swallow tail. They create a different pivot point on the board for a different type of control.

I guess it's just another variation that has evolved for a bit of variety in the surfboard's flow on the wave.