Question

What is the difference between negativa voltage and ground?

Answer 1

ground means zero potential...

Answer 2

Voltage is always measured between two points. A negative voltage measured at A, with respect to B, means if a wire is connected from A to B then positive mobile charge will flow towards A, and negative towards B.

"Ground" is a shorthand way of specifying a reference point for many voltage measurements. In a piece of electronic equipment, it is often the chassis. In the case of electrical equipment, like a transmission line, it is often literally the ground, meaning the dirt under the towers. Quite often electrical circuits are designed so that all return paths to the ultimate source of electric potential -- a battery, or generator -- go along some common pathway, e.g. through the chassis of a piece of electronic equipment, and this return pathway is called "ground" and serves as the common reference point for all voltage measurements.

It's unusual for electrical distribution systems, like transmission lines and such, to rely on the literal ground (the dirt) for the return path of the electricity, because it's difficult to ensure that this path is sufficiently uniform, has a constant resistance, et cetera. Usually you provide an actual return path, a wire, although the voltage of this wire with respect to the actual literal ground may be near zero, i.e. it might as well be connected to it.