The term 'Wharf Denizens' refers to the people who inhabit wharves, which are docks or piers used for loading and unloading ships. One of these denizens is rats, which have four letters in the crossword solution. Rats are often found in and around wharves due to the abundance of food sources, such as discarded food from ships and garbage from nearby restaurants. They are also attracted to the warm, damp environment of the wharf.