What Is Science?

What is science?

What is science?
I don't really know. Science is what I do for living. I do research, and I get paid for it. But I don't really know what science is.

I might say that science consists of our understanding about the universe. Science is also an activity to improve and to expand our understanding.

But what is understanding?
What do you mean, when you say:"I understand"?

For me, that's the most difficult part in science.
I don't really now what's understanding mean.
And if I don't know the meaning of "understanding",
then I don't know the meaning of science.