Karma is a Sanskrit word and it means "Action", Hindus in the past have concluded that we do four things in the entire life, (1) Eating (2) Sleeping (3) Making Babies and (4) Defending(fearing). All our daily activities are rooted in the four result oriented actions and all actions are directly connected with three modes (1) Intelligence (2) passion and (3) Ignorance.
(1)If action is performed in the mode of intelligence the result we obtain is positive, almost 100% guaranteed, in short we get what reasonably we expect.
(2) If action is performed in the mode of patience, the result we obtain is "fruit of activity" it means if we grow Potatoes we do not get onions.
(3) If action is performed in the mode of ignorance, that results in "Blind Risk" it's a gamble or luck. If negative it may irritate, creates enxity, get upset, get mad.
Unfortunately, many people in the world either misunderstood Karma or understood a portion of it, so most of the people are saying "Good Karma and Bad Karma" and so on....I believe " good or bad" is dirt of mind.
I can talk on this subject for hours and years but in short, this is what I understand about KARMA, I hope you will think about it and forgive me if I am wrong.