Santosha is the Sanskrit word for contentment. In yoga practice we learn to choose it instead of other ways of being. Letting go of attachment to unmet desires releases us to choose well.
I like to think of it as putting on clothes. I could wear my old baggy pajamas and my stained and torn sweatshirt. Or I could put on something lovely that feels good and is uplifting to me and others who might see me.
To what unmet desires are you attached? Are you willing to release them? Ki to Happiness chooses to put on Contentment.