Electrostatics is the theory of the electric field in conditions in which its behavior is independent of magnetic fields, including
The electric field associated with fixed distributions of electric charge
Capacitance (the ability of a structure to store energy in an electric field)
The energy associated with the electrostatic field
Steady current induced in a conducting material in the presence of an electrostatic field (essentially, Ohm’s Law)
The term “static” refers to the fact that these aspects of electromagnetic theory can be developed by assuming sources are time-invariant; we might say that electrostatics is the study of the electric field at DC. However, many aspects of electrostatics are relevant to AC, radio frequency, and higher-frequency applications as well.
Additional Reading:
“Electrostatics” on Wikipedia.