The net charge of a system of particles is the sum of the charges of all the particles in the system. If we combine equal amounts of positive and negative charge we obtain zero net charge. The net charge of a system is a conserved quantity. Net charge cannot be created or destroyed. We say that charge is conserved .
Atoms are neutral particles.
They have no net charge. The charge of the nucleus is exactly canceled by the charge of the electrons. We have exact cancellation, because charge is quantized. The number of electrons in a neutral atom equals the number of protons. The charge of the nucleus is Ze.