Joy is not just a state of mind. It is not a fleeting emotion. Joy is a very real force, and the devil doesn't have anything that can stand up against it. Just as fear has to yield to faith, discouragement has to yield to joy.

Whatever circumstances you are facing today, you can be full of joy. You can be strong in the Lord. You can draw on the supply of the Holy Spirit within you and come out on top.

Definition Of Joy: "the emotion of great delight or happiness caused by something exceptionally good or satisfying; keen pleasure; elation: She felt the joy of seeing her son's success.
http://dictionary.reference.com/browse/joy

Your definition is correct but joy from this context as stated in my post above is more than just being happy. or being, delighted it is a force that strengthens every part of you Body, Spirit and soul. We know in the scripture quoted “the Joy of the Lord is my straight" this makes us to understand that Joy is Strength, and the Joy of the Lord is a product of revelation that ignites an understanding and brings joy (Strength) to your entire being.

This is one thing that makes Christians different from every other kind of being. This is because righteousness, peace and joy in the Holy Ghost are products of being in the kingdom of God. We have an assurance that no matter what happens we have this peace the world can not comprehend, we have Joy unspeakable. That means u can not define it using the best kind of dictionary.

This Joy is not by how much you have or how much mistakes you have made but how much of God's glory you are going to experience both in this world and the world beyond. it would only take you to have deeper Knowledge of God's word to grow in this joy.

He is talking of joy unspeakable full of glorious things!
the joy that draws beautiful things from the well of salvation!!
The joy that gives strength always!!!

Inside, you're perfect--born again in the image of Jesus Himself. But outwardly do you find yourself falling frustratingly short of that perfection? Is there a solution? Yes! The secret lies in "the renewing of your mind."


http://www.kcm.org/studycenter/devotional/f2f/index.php?l=eng