Anyone know what the on/off toggle switch in this picture is?

the89tiger

It is just to the left of the StabilTrak button...

jesgetme

looks like maybe the owner before you had a system. Might be a power switch for the amp.

stever

Now that I think about it, I saw a Prius a year ago in a showroom that had two switches that looked like that. The dealer had added an aftermarket heat kit for the front seats.

So @jesgetme is on the right track - it looks like something aftermarket. Notice how the trim bezel is different than the traction control button.