if i can define happiness as a positive psychological condition, its defining features may include three major aspects, corresponding to the three terms i have used to describe it.
for one thing, happiness must perforce be a 'positive' experience: whatever makes you feel 'good', desirable, enjoyable or pleasurable naturally offers you a sense of happiness, or serves to endorse your sense of it. such being the case, there is a whole wide range of objects and situations that can happify your life, such as food, music, dance, sports, work, travel, play, chatting, sightseeing, viewing movies/pictures/good-looking humans, reading, thinking/imagining, creating, daydreaming, sleeping, love-making, and even crying (over a tragedy, for instance), among many others. that is to say, one can theoretically get happiness from anywhere, by doing anything, or at any moment. as long as you are enjoying yourself, as long as you enjoy being yourself, you are happy. it is as simple as that.
two tendencies must be taken into account insofar as this positiveness goes:
quantitative to qualitative: a particular physical object or activity may give you only one particular happifying experience, but with enough such experiences, you may rebuild yourself and become happy 'by nature'. those who seek happiness by trying to obtain as many such physically pleasurable experiences as often as possible are what has traditionally been called 'hedonists'. needless to say, most people simply cannot afford to be happy this way.
transient to constant: all physiological or sensual experiences are transient or ephemeral. only when you construct your happiness on the intellectual level with enough physiological or sensual experiences can you attain a constant or sustainable sense of happiness.
in a word, happiness is a positive experience, which can be attained in a transient, physiological and quantitative way at the lower level, and sustained in a constant, intellectual, and qualitative way at the higher level.
most people tend to measure a person's success in terms of money; for me, success, no matter how it is defined, can always be measured in two ways:: on an individual basis, it is determined by the extent to which one is happy about one's life; on a social level, success should be measured in terms of how much positive change an individual has introduced to the human world, or how many other people's lives one has functioned to improve.
unlike longping yuan, deng xiaoping, bill gates or steve jobs, i have improved very very few other people's lives besides my family members', so i am far from successful in a social sense, but as an individual, i feel i am exceptionally successful because i believe i have found not only true happiness, but also even the secrets about how to become a 'god' or buddha upon death.