Karma is a Sanskrit word meaning action.  

It means any action you do, whether it is physical, verbal, or mental.  

Take a guess: how many actions do you do each day? 

Buddhists say we each do 65 actions per second, constantly, all day long. It may be a fleeting thought, a judgment, a touch, a glance, a word muttered under your breath. Of course, it can also be something big like saving a child's life or just hauling yourself up out of bed in the morning to go to work. 

Can you imagine how many actions you rack up in a day, at the rate of 65 per second? There are 86,400 seconds in a day (there is some controversy about whether you make karma while you're sleeping; so, discounting 8 hours of sleep, that's 57,600 seconds of waking time.) 

So you do 3,744,000 acts per day (57,600 seconds times 65 acts per second).  

How many of these are you conscious of? 

An action creates a seed in your mind that lies fallow until something triggers it. After a lifetime (averaging 72 years, worldwide), we've built up a bank of karma of 98,392,320,000 seeds, just waiting to go off.  Depending on the kind of life we've led, they're a mix of good and bad seeds. Maybe some proportion of neutral ones as well. 

Then, of course, Buddhists say we each live many lives. Maybe a couple million. So multiply that by a couple million. Or more. 
 
Our lives are overfull of cases of what seems to be injustice, where sometimes bad things happen to good people. Often we lament that there is no justice in the world. The laws of karma tell us differently. They say that every kindness is rewarded. It just might take a couple of lifetimes. But it's comforting to know there is justice in the world. And there is a way, Buddhist tradition tells us, to manage karma so you get more good results during your lifetime. 

So--what makes a karmic seed go off? What happens when a seed opens? How many seeds open and are discarded in a lifetime? How many remain to be carried over into the next life? How many seeds do we bring into this life with us? What characterizes a good seed and a bad seed?