Karma is simply a score determined by the frequency and type of activity you perform in the app. Coins are awarded upon reaching levels of Karma starting with 100 and increasing as follows: 250, 500,1000, 5000, 7500, 10000, 15000, 20000 and every 10K additional from there on.
Please note that anyone abusing the Karma system will be docked accordingly - read more.