1 [uncountable and countable]
when something or someone enters or passes through something, especially when this is difficult:
Cover the entire device to prevent water penetration.
The attack failed to lead to any deep penetration of enemy territory.
2 [uncountable and countable]
the degree to which a product is available or sold in an area
the rise in import penetration of the domestic market
when a system of beliefs enters a society and becomes accepted
the penetration of Marxism into Latin America
when someone joins and gets accepted by an organization, business etc in order to find out secret information
foreign penetration of the British secret service
when a man puts his penis into a woman's vagina or into someone's anus
a special ability to understand things very clearly and completely