A more thorough explanation:

DECREMENTUM MARIS

Decrementum maris is a Latin term that means the decrease of the sea from the land.

During low tide, the water level decreases and the shoreline expands, which is an example of decrementum maris.

Another example of decrementum maris is when a beach that was once covered by water during high tide becomes visible as the water recedes.

These examples illustrate how decrementum maris refers to the receding of the sea from the land, resulting in a decrease in the water level and an expansion of the shoreline.