"Scientific works which researches mankind's positive states of mind." This is my own definition after I read some articles.
"Positive Psychology is the scientific study of the strengths and virtues that enable individuals and communities to thrive. The field is founded on the belief that people want to lead meaningful and fulfilling lives, to cultivate what is best within themselves, and to enhance their experiences of love, work, and play." And this is more professional type of describe which exist on Penn website.
Shawn Achor is an American educator, author, and speaker known for his advocacy of positive psychology. Achor spent ten years teaching at Harvard University, where his "Happiness" course became one of the most popular courses on campus.
Spotlight: Big Think, Question and Answer
Question: What is positive psychology?
Shawn Achor: Positive psychology is a movement in social psychology which attempts to change the way that we think about humans. Instead of focusing merely the average, which is what we normally do in traditional psychology, we would find out what the average person is like, or how the average person responds. Instead, what we look at are people who are up above the curve for some given dimension. Maybe that means that they are extremely energetic, that they are very happy, they’re very productive. And our goal is to find out why that is.
Question: How is this different than self-help?
Shawn Achor: I think a lot of the self-help movement is based around people who have a great idea where they think that some things worked out very well for them and they try to press that upon other people. And sometimes that advice can be very helpful and very sound, but what we’re interested in studying in positive psychology is what’s actually going on inside the human brain. What happens to an individual if they took that advice?
footnote: I took some part from article. I advice you to read whole chapter from Big Think website.

