Question: An entity is an "object or thing" in the real world distinguishable from other objects (see the explanation of entity-relation model in the textbook).

What is an object that exists and is distinguishable from other objects?

An entity is an object that exists and is distinguishable from other objects.

Is a thing or object in the real world?

Real world objects include things like your car, TV etc. These objects share two characteristics: they all have state and they all have behavior. that they, too, have state and behavior. A software object maintains its state in variables and implements its behavior with methods.