an atom is said to be charged when there is an imbalance between its number of protons and electrons.
additional information
units of charge
charge is measured in SI unit \(C\), coulomb. However, we are often dealing with \(e\), the charge of an electron (as ultimate that’s the principle way by which charge moves around). \(e \approx 1.6 \times 10^{-19} C\).
net charge can be neither created nor destroyed
Unsurprisingly, though you can move electrons around, they will be conserved across a system.