What is The Matrix about?

Before that:

What's reality for us?
Let's suppose say, it is what we perceive.

How do we perceive?
We perceive via our senses, hearing, seeing, touching, tasting, etc.

How are these senses sent to our brains?
Via electrical signals through our nervous system.

Now what if we provide these signals artificially from outside. How would our brains identify that these signals are artificial (assuming the signals are simulated perfectly)?

Matrix is the system, which simulates these signals and feeds them into the humans connected to it, thus making their human subjects believe that they are perceiving ...