See some of my essays and talks on hygge here.
I did PhD and post doc research on hygge. I carried out extensive ethnographic research on how Danes relate to home, togetherness and family life, and how hygge influences the consumption of leisure, hospitality, food and drinks.
I define hygge as the experience, in a particular situation, of social relations and physical conditions that allow one to be present, in a way that feels unhurried and authentic.
One could also define hygge as an atmosphere that allows dwelling. My definition of hygge has simplified over time, as I have worked with the topic from different angles. Read earlier thoughts on a definition here.