Karma, what's that?
As defined by Wikipedia, Karma is the concept of "action" or "deed" in Indian religious understood as that which causes the entire cycle of cause and effect (i.e., the cycle called samsara) originating in ancient India and treated in Hindu, Jain, Sikh and Buddhist philosophies.
Wow...what a lengthy, indigestible definition!
In my own innocent, layman term, it just means that "whatever actions you take will affect how others treat you in future". A simple illustration.

Though I am not a believer of any religion but I do believe in karma. I maybe suffering in the hands of someone now or my life maybe miserable now or I may feel that my dreams have not been realised, but I may not despair. Because life is a cycle, like the stocks and shares. When there are ups, there will bound to be downs. When a person gets unlucky now, he/she will get lucky in the future, that is life. And when a person performs good deeds, he/she will be rewarded.
Take Michael Jackson for e.g., he was at his peak of his career for a few decades; enjoying the fame and wealth that everyone of us yearns for but look what happens in the end? His career went into a pithole, deeper than anyone of us could imagine. Perhaps, I sounded very sceptical, but this is life, whatever goes around comes around.
Another cute e.g. will be that of my colleague. She used to be an auditor. Those in the accounting line or who have worked directly with auditors, will understand how irritating and how unwelcome these people can be. They will disturb you when you are at your busiest moments and request for information or documents that seemed to be totally irrelevant to the accounts - just because their accounting rules and regulations say so. So she quitted being an auditor and switched to a career whereby she is now constantly being chased by the auditors. See what I mean? Whatever goes around comes around.
However, I realised that human beings are such funny creatures. Though we understand what karma is and how karma works, most of us are still doing things that are against the energy of karma. Why is that so? Why are we always allowing our emotions to rule our actions? Why do we often have to regret only after the actions have been done? Something which I have yet to understand...