Well google says happiness is the state of being happy.
What @Cyan thinks:
Well happiness to a lot of people is money. But money isn't happiness it is just a distraction from being depressed about being sad. The key to happiness is love in my eyes. If you find someone who would put you before anyone including themselves like you do them than that is all you need in my life. If that man/woman loves you he/she wouldn't leave you when you failed, he/she would help you succeed in life. I know from first hand that the love of my life feels the same for me as I do her, and we don't need money to be happy. We just sit at home and cuddle and eat pizza and watch free movies. Happiness is the key to success, if you aren't happy you need to change something.