(Skip down to the definition at the end, if you wish, or just read this through for a bit more understanding.)
What is it actually, in simple terms?
So many people think of it as some high unattainable state of being, like true enlightenment.
But it is quite acquirable in a practical way.
So, let's get on with some simple illustrations of what it is, so that you can see it's attainability.
IT'S A CONVERSATION
All of anything you do in life is a conversation. (Now isn't that a wise statement!)
And the way most internal conversations are started off is with a question.
It could be something as simple as "what shall I do next?" And then you could just do the first thing that came to mind from the Monkey Mind (see How The Mind Developed). Often that would not be wise, as it is random and not on purpose. Wisdom is thinking on purpose to bring about into reality a purpose (something wanted).
A wise person would ask, assuming we are thinking of something besides what to do next in the kitchen:
1. "What result do I want?"
2. "Is it worth the effort I will put out?"
(You see, wisdom is a skill to learn and skills involve learned processes - such as asking questions and doing things in a productive sequence. At this point, one might observe that this is a lot like Problem Solving. Not like a bad problem, but like there is a gap between where I am and where I want to be so I have the problem of solving how to close the gap - more like a math problem in school.)
"That which can be effectively applied to gain what is desired and valuable."
It is about practicality and results, not about fancy talk, philosophy, or theories.