Well, anyone who does not know will soon discover the hard truth and meaning of karma as soon as they wrong or try to wrong anyone, familiar or not. I am writing from my own experience lol!
I used to say just what I think about any given person or situation, good or bad, not really having a filter. But i've realized that the bad things I say would come back to me. Like speaking bad about someone might mean the bad words would turn around and come straight for me, like a put a bad spell on myself. Or treating people in a not so nice manner as we all have done at some point. A fine example of this would be for example: you are at a grocery store and the cashier gave you more change than you should have gotten and you keep quiet about it. The right thing to do would be to speak up, otherwise the poor cashier would have to pay the till shortage out of their own pocket by the end of their shift. Soon, very soon my fellow readers, you will realize that you find yourself in the same shoes of the cashier, having to pay for some unexpected bills, getting a stupid fine or having to fork out money for unforeseen circumstances. By this i don't mean general emergencies, i mean paying for something that could have bee avoided had you done the honorable thing in the first place and be honest about your extra change. Another example of karma getting back at you would be laughing at someone who fell only to find yourself slipping on the floor the next day in the mall.
In short karma means what ever bad you do to other people would come back to you 7 times worse than what you did to the other person.