What is Ionization Enthalpy

What is Ionization Enthalpy?
The enthalpy change associated with the removal of the first electron from an isolated gaseous atom in its ground state is called the first ionization enthalpy.
The ionization enthalpy of an element can be defined as the amount of energy required to remove an electron from an isolated gaseous atom in its gaseous state. Ionization enthalpy depends on the following factors:

Penetration effect
Shielding effect
Electronic configuration