What is exactly the “negative” charge?

If we take a particle, a non neutral one, we know we can measure a distribution of charge on it. Now, the fact that this particle may have positive distribution of electric charge it's ok. Maybe because we (I) are all get more used in thinking about real positive numbers more than negative ones.

But when we measure a "negative" distribution of charge.. what is really "negative"? How a change can be negative?

• replace negative, neutral and positive by white, grey and black. The sign of the charge is a kind of flag. It is convenient to use the + and - because of the annihilation relations – user46925 Dec 5 '15 at 4:09