Back up camera connection

[Mnfmkf]

Literature supplied with camera states to connect red wire from camera to hot wire that goes to the back up light.
From reading this wire is found in the rear compartment and is light green.
Ok I understand that,

Then it states to connect the black wire coming from the camera to the negative wire. . ... That's where I am missing the point.

Is that a ground or does the car actually Have a negative wire ?

Help is appreciated here..
Thanks mike

[RED_DET]

I would assume ground, but haven't hooked up a camera before.