Of course, it only happens when I am content, and even then I only notice it maybe once every several months. It has happened a few times, though, and it was quite a stark emotional high. But to answer the question, I guess happiness would be the knowledge that your life is the way you want it to be, more or less, and you don't have any serious voids in your heart. I don't know. I could get poetic.
Happiness is the perfect harmony of good music on a lazy afternoon.
Happiness is your first ice cream cone, your first paycheck, your first kiss.