What is the difference between a pier a jetty a depot and a quay?

A pier is a structure that extends into a body of water, used for such purposes as tying up boats (or ships) and/or loading and unloading cargo.

A jetty is a strip of land or rock, often built in pairs, that maintains a harbor or channel.

(Where it actively limits shoreline waves, it may be called a breakwater).

A depot is either a train or bus station, an area for storage (warehouse), or a military installation.

A quay is a wharf, a platform over or adjacent to a river or body or water that serves in loading, unloading, and storing cargo.