What did zeroing artillery on invasion beaches mean?

What does it mean to say that an invasion beach had been zeroed by artillery?

The batteries already knew the target coordinates and firing data. They could register again if their own bombardment changed the beach's geography.

British batteries knew the coordinates of likely landing areas and could prepare their fire in advance. Heavy bombardment could alter the beach itself, requiring the guns to be registered again against the changed ground. Mobile artillery units were also assigned to meet an invasion. Possible supporting fire included 14-inch guns at Dover alongside field and coastal weapons.