What is happiness? Good question!
What is suffering? What is Happiness, What is Suffering? Well, suffering, I think we know a little bit better, right? Nobody wants to suffer, not a single sentient being. From humans to little animals, nobody is looking for suffering. But, we don't know how to recognize suffering, where it is. Sometimes what we call "happiness" is in fact suffering. We don't know the causes of suffering, the obvious causes of course, but there are some hidden ones: ignorance, attraction, repulsion, hatred, jealousy, pride. Of course these are mental toxins that bring up suffering. So, what is happiness? Ultimately, it's the complete freedom from mental obscurations. Enlightenment! Now of course this is a tough call for most of us, but you know, there's a long way. It's not everything or nothing. Every step on the path in the right direction gradually erodes the causes of suffering, as you get rid of animosity, pride, jealousy, strong obsessive desire from your mind, to that extent you diminish the cause of suffering and every moment of life becomes more enjoyable. So it's a matter of degree. Then, when you achieve enlightenment, as His Holiness says, complete rest. Until then, constant effort.