What the hell is ISO?

I always want to know what was that ISO thing in digital cameras. Now, I know. Great guide.

"As I prepared to take my first photo, I found that the camera was so starved for light that it wanted to set the exposure at about 1/10 second–far too slow to get a sharp image of active animals, especially since I was hand-holding the camera.

So what did I do? I increased the ISO."

Link to the article: Use ISO to Take Low-Light Photos