What is happiness?

Is happiness tangible and measurable or an arbitrary state of mind? Is it something we actually have or just think we have? Can it be only either present or absent? Or are there different degrees of happiness? Is happiness an ideal state that we continually work towards? Or is it a comparison in our own minds ("I'm happier now than I was then") so that we will think we have achieved happiness if we are the happiest we ourselves have ever been? Or is it what we think we are when our lives are better than those around us ("I'm happier than he is, so I must be happy"). Or, is happy just a generalized word to encompass many more specific other emotions (such as proud, valuable, excited)?

I have always wondered if there was a correlation between the amount of endorphins released from an activity (running, a movie, sex, food) and our willingness to pay for it. This could be a way to measure actual happiness, by the amount of endorphins released. Utils could become measurable as "number of endorphins released." But still, some people that have never experienced the greatest happiness would be happier by the little things, but maybe not willing to pay as much because so many things make them happy.

Bill McKibben argues in Deep Economy that people who call themselves happy actually or have higher electrical activity in certain areas of the brain, are more likely to be rated as happy by friends, less likely to be involved in disputes at work, and less likely to die prematurely. In this way, he shows that we could use these correlations to provide a tangible and objective measurement of happiness. But to me, these correlations seem to provide more benefits of happiness, not a definition of what it is or how to achieve it.

Whether happiness is tangible, objective, and definite or just an arbitrary ideal state of mind, it is still an arbitrary ideal state of mind that I would like to have. Even if happiness is subjective, many of us still want to achieve it.