What Defines Happiness?

Often times, I tend to over think things. A LOT of things. From financial situations, to romantic situations, to family and future situations. Doing that does often result in stressing myself out, which is very unnecessary. One of the biggest things I tend to think to myself is, "Am I happy?" I tend to overlook whats going on in my life at the time, like the people I involve myself with, as well as how much my family members are currently doing. I even take into account the amount of money I have in my pocket. Its always a toss up, because I can never truly convince myself I am happy. I may be currently satisfied, or not sad....but I cant really say "happy." Maybe because I don't really know what that words means. Do you? Is there an exact definition to that word, or is it different for everyone. Do you need to have a smile on your face to be happy? Does EVERYTHING have to go the way you want it to go in order to be happy? I tend to lean more to the "everyone has their own version of happy" side. I've known people who were more than set financially to have any money worries, yet they didn't seem in good spirits. I've seen families with next to nothing but a roof over their head, but be all smiles because they were still a loving family and were all together. I think at the end of the day, "satisfied" and "happy" tend to get mixed up. You can be successful, but alone. Or with a loving family but no material things. I'd like to think that happiness is as simple as being optimistic and grateful of everything, but like I said...I don't think I know yet what happiness truly is. But I am grateful for still having my family and friends in my life, which right now is all I need to get by.