According to https://www.merriam-webster.com, the definition of happiness is a: a state of well-being and contentment: joy b: a pleasurable or satisfying experience.
http://www.dictionary.com says that happiness is 1. the quality or state of being happy.
2. good fortune; pleasure; contentment; joy.
In The Book of Mormon, King Benjamin gives a great address to his people in which he makes the following statement; "And moreover, I would desire that ye should consider on the blessed and happy state of those that keep the commandments of God. For behold, they are blessed in all things, both temporal and spiritual; and if they hold out faithful to the end they are received into heaven, that thereby they may dwell with God in a state of never-ending happiness. O remember, remember that these things are true; for the Lord God hath spoken it." (Mosiah 2:41)
As you know, one of my favorite LDS speakers is the apostle Elder Jeffrey R. Holland. In September of 2014, he gave a devotional address to the students of BYU-Idaho titled, "Living After the Manner of Happiness." This is the resource I would like to share today to help in the ongoing "quest" to overcome depression and anxiety. You can find the transcript here: http://www2.byui.edu/Presentations/Transcripts/Devotionals/2014_09_23_holland.htm