Happiness is and can be many different things, to many different people, during many different times of their lives.
There have been many quotes made in the past by many famous people defining their concept of what happiness is for example: "If you want to live a happy life, tie it to a goal. Not to people or things," by Albert Einstein; "Happiness is like a butterfly: the more you chase it, the more it will elude you, but if you turn your attention to other things, it will come and sit softly on your shoulder..." Thoreau.
Thoreau in his comment seems to be saying that happiness is elusive, if we try to find happiness it runs away, yet if we just sit back and wait patiently, it will find us. Einstein in his comment seems to tie happiness to goals in life. If one wants to be happy one needs to have certain things planned to attain happiness. These two statements seem to contradict each other. Thoreau says wait and happiness will find you, yet Einstein wants to tie happiness to concrete things.
Yet again, have we really defined what happiness is? Can happiness even be tied down to a definition or is it still going to be elusive like Thoreau's butterfly.
Happiness in my opinion can not be confined to any one specific feeling or definition just by the nature of the word "Happiness". Happiness is elusive, she is mystical, and she always seems to be just out of reach, like a leaf floating on the wind.
So let us look at this from another perspective. To me the best way to define what happiness is, is to look at oneself, to examine your life, your soul, your surroundings and see if you are happy with what you have or don't have.
To be truly happy you need to feel that you are making your best efforts, no matter what your efforts are in. The feeling of achievement when you accomplish a difficult task is a natural high.
Even with the feelings of being successful, ephemeral though they are, without a positive mental outlook, I don't think you can recognize or appreciate happiness. Happiness doesn't run up and down the street yelling "stop and pay attention I'm happiness". It sneaks up on you in the quiet moments that Huxley's "Brave New World" would have denied you.