What exactly is an "electric charge"?

Here you'll be blind again. What's the charge? You can look at the previous definition, here we think of charge as charged particles, that is, electrons, after all, in the metal conductor can move inside the free electrons, that is, electrons. So our understanding fits the theory.

In fact, the most reasonable explanation should be: charge can be regarded as a charged particle, the free electron is the carrier of charge, just like the object is the carrier of the quality of this property, the movement of these carriers is the most essential reason for the formation of current. The electron is just a carrier, and the real effect is the charge, which can form an electric field behind the accumulation, which can push the electron. So our textbook theory, all the time, says that charge works, but it doesn't say why charge works at all, and the textbook is right, it just doesn't spell out the nature of charge, it doesn't convey it.