Bar – Where a spit grows across a bay, a bay bar can eventually enclose the bay to create a lagoon
She sat at the end of the bar and spat. The spit went right across into the bay window.
A bar results from the further development of a spit.
Longshore drift moves sediment along the coast, but when the coast suddenly changes shape, going into a bay, the sediment is deposited at the "corner".
Over time, this deposition grows into a spit, and over even more time, it grows right across the mouth of the bay, becoming a bar.
The water in the bay then becomes a lagoon, cut off from the sea.