What do you mean by shielding and penetration effect

What do you mean by shielding and penetration effect and is there any relationship between them?

Penetration and shielding are two underlying principles in determining the physical and chemical properties of elements.

Penetration describes the proximity of electrons in an orbital to the nucleus. Electrons which experience greater penetration experience less shielding and therefore experience a larger Effective Nuclear Charge (Zeff) but shield other electrons more effectively. Electrons in different orbitals have different wavefunctions and therefore different distributions around the nucleus.

Shielding describes the amount of screening from nuclear charge that one electron can do with respect to its neighboring electrons. Electrons that have greater penetration can get closer to the nucleus and effectively block out the charge from electrons that have less proximity. For example, Zeff is calculated by subtracting the magnitude of shielding from the total nuclear charge. The value of Zeff will provide information on how much of a charge an electron actually experiences.