What is the happiness? Hmmm... It's a difficult question and I'm definitely sure that happiness can't mean the same to all the people.
May be for elderly people who have lived a long life it's easier to find an answer for this question, but nevertheless I'll try to give my own understanding of this phenomenon.
Happiness is something that lives inside each of us, but not all the people are able to feel it. You can neither buy happiness, nor sell it; you can never win it in the lottery; the only way to be happy is to grow your happiness. Have you ever noticed that some people are always grumbling about their endless problems, dissatisfaction in life and even about the dull weather that annoys them? Such people see only dark sides in everything and it prevents them from being happy. But look at other people! At first sight they have nothing in life; they don't have stable jobs or their own apartments, but they are really happy; they meet every day with a smile, they laugh and receive pleasure from life. Isn't that great?
I personally appreciate such people and I believe that happiness is to live your life, to enjoy every day of your life, to be glad to every minute and to receive with thanks everything that life offers you. And even when it gives you hardships and difficulties, it gives you strength to overcome them. Happiness means to live your life in such a way that when retired you have something to remember and to be proud of, some pleasant moments that will always evoke a smile.
I'm sure that I'm a happy person: I have many friends, loving parents, goals in my life, etc. As one of my friends says if you are not a handicapped person you are a really lucky and happy one. And I think that is true. I try to enjoy every day of my life and be happy all the time: to smile when I wake up because of the bright sun shining directly into my window, to feel happiness somewhere deep inside playing snowballs or swimming in the sea, to feel pleasure when I see a child happily laughing or when I look at a large rainbow after a downpour. So be happy!