I have searched but the explanations that are given are too abstract. Why is it so difficult to use an example to show what a Borel set is?

Assume X = {1, 2, 3}. Then the power set of X is a topology. Borel set is defined on topologies right?

So what would be then a Borel set?

Or perhaps someone could explain to me without the above example, but in clearer terms what a Borel set is?