Understanding the concept of "Entity"

Question

I was reading the concept for an entity, it says:

An entity is something that exists as itself, as a subject or as an object, real or potentially, concretely or abstractly, physically or not. It need not be of material existence.

But, in fact, all we think about exists in our minds, so is everything an entity? Why does the concept of an entity even exist?

Answer 1

Entity is something that is capable of performing an action on its own as some level of abstraction.

A machine is not an entity as long as it is, well, mechanical. A machine that can "think on its own" as in choose, reject other than on pre-built mechanism fulfills requirement of an entity. AI would be an entity.

Sunlight is not an entity, it cannot choose to act differently on same kind of objects. There is no freedom of action given, no agency.

The Creator Of All - the first cause - is an entity. He do what He do on His own.

"All we think about exists in our minds". This is pure wrong. You are mixing two things. What you think about may exist independent of you. You can think about sky. If you never exist sky will still exist. Its your thoughts that exist in your mind. If you never exist your thoughts never exist.

Answer 2

In general, in philosophy, entity is part of a set of interrelated terms. This following list is the result of personal experience, consider this answer just an opinion; the dialectical approach simplifies its understanding:

• An object is the counterpart of the subject in an interaction. It is any whole which is not the subject. A subject is an observeR, an object is an observeD.
• An entity is the equivalent of an object that exists by itself (from Latin ens: to exist). Notice the difference: if an object needs of a subject to exist, an entity is considered to exist by itself.
• A being is usually the same thing as an entity.
• A thing is mostly a physical object, although the definition of thing is very loose.
• A system is commonly an entity, approached from its structural perspective. Strictly, system means a set of interrelated parts; notice that such definition is recursive/fractal: any system is a set of parts and any part is a subset of a system.
• A set is a collection of objects; notice the difference with a system: while a system is a set of related parts, a set does not approach relations.

In all concepts, it is important to consider that:

a) All boundaries are subjective. A mountain can include or not the rocks 10m below its base; a wave can include or not the water drops around it; a house can include or not part of the street; an apple can include or not the water molecules that had just evaporated a nanosecond ago, a person can include or not its clothes, a rainbow can include or not the sunlight, etc. This means that perceiving a circle implies perceiving two domains: what is the circle and what is NOT the circle.

b) All objects essentially exist in our mind. Outside of us, the rainbow, the river, the rock, the sea, etc. is just a set of molecules or atoms that has no boundaries with the rest of atoms of the universe. A martian having the size of one atom would not be able to know an apple (how would he know the boundaries, which finally are human ideals?). However, some philosophical perspectives accept that objects exist as independent things, without need of the perception of an observer (see metaphysical realism).