The following definition of Karma's what I found online.
In Buddhist teaching, the law of karma, says only this: `for every event that occurs, there will follow another event whose existence was caused by the first, and this second event will be pleasant or unpleasant according to if its cause was skillful or unskillful.'
A skillful event is one that is not accompanied by craving, resistance or delusions; an unskillful event is one that is accompanied by any one of those things. (Events are not skillful in themselves, but are so called only in virtue of the mental events that occur with them.)
Therefore, the law of Karma teaches that responsibility for unskillful actions is born by the person who commits them.

Chim? You bet! But basically, I personally just summarise all those into that all-too-familiar saying "You Reap What You Sow."

Karma nowadays is something over-used as a convenient excuse to explain something that's vaguely diffcult to explain. Everything can be attributed to Karma. Why so? Karma preaches the significance of cause and effect. People, however, abuse this idealogy and use Karma as the reasons ('cause') for events ('effects') that happen for convenience sake.
For example, if this woman's abused by a horrible stepfather and equally abusive mother since young, and she eventually turns to Buddhism because Karma is in fact, a logical reason to explain the brutal unfair unreasonable attacks she has suffered since infancy.
To me, it's perhaps denial at its most extreme. Refusal to accept fundamentally flawed families. Refusal to accept reality. Others may go as far as to say it's dangerous brainwashing because in such cases, victims find a way to forgive their abusers and these criminals get away scot-free, ready to inflict pain and suffering on hapless others.

And then there is the beginning. Somehow, Karma has to start at some stage doesn't it?
Do we start off as humans or animals? Is it like some roulette of destiny whereby it's by luck which 'body' you first inhabit?
Are there a limited amount of entities in the world since we all technically, have lived once or more?
If so, as the global population continues to expand, does it mean more animals are being reincarnated to be reborn as human beings? Or is the situation like a factory, churning out more new unique entities second after second?

Chicken...? Or egg?