According to Wikipedia, A lazy Susan is a turntable (rotating tray) placed on a table or countertop to aid in distributing food. Lazy Susans may be made from a variety of materials but are usually glass, wood, or plastic.
Simple interpretation is that the lady at home must be very lazy and didn’t like to move around serving the food going from one chair to another. So this was invented to avoid this. Eaters could rotate it to scoop out the food.
During earlier times, it was also called a Dumbwaiter. Both Dumb and Lazy parts have almost similar connotations. But where from the name Susan came? It is an english name. When this contraption was invented, the name was hardly popular. So the name origin is still debatable.
Incidentally, it is very popular in chinese eateries where it made the Dimsum eating very simple.