what is called a rectangular concrete beam not supporting any slab/load ? Is it a drop beam?

There is no terminology for a rectangular concrete beam not supporting any slab/load.

However, A drop beam is installed perpendicular to the joists (the horizontal boards or beams that support the framework) on any structural member. For example, if a row of joists is positioned north to south, the drop beams run east and west directly beneath the joists, providing them with a firm layer of support.