1967 mustang please read detalis?
It means that the car is an automatic, but has a manual valve body installed in it. The valve body is a set of passages in the transmission that change the gears by releasing the clutch pack when hydraulic pressure passes through them. A "manual" valve body is just that- you have to engage a mechanical switch to change gears. Thats where the bump shifter fits in. The shifter should have a spring loaded, ratcheting type of action that will pull on a cable connected to the transmission. Push the shifter forward you upshift, backwards you downshift. A properly built automatic transmission with a manual valve body will shift faster than having a standard manual and thats why they're popular in drag racing. If the car's got lower gears and a bump shifter, it's been raced and probably gotten the crap beaten out of it. You might wanna look for something else, something close to stock or all stock. A used car is already someone else's problem.