Pressure Canner vs pressure cooker
A pressure cooker basically has two settings, high (about 12.5 psi for electric, and 15 psi for stovetop) and low (4 to 7 psi). There are no gauges to accurately specify the pressure in pressure cookers.

Pressure canners, on the other hand, are generally larger, and are equipped with accurate gauges so that the user can measure the exact pressure inside the pot.  It is this accurate measure of pressure (and time) that is necessary to safely can food.