Where there is fear, there can be no true happiness. Where there is fear, there can be no freedom. I like this short video of Thich Nhat Hanh discussing what is Nirvana.

"Non-fear is the true foundation of great happiness. As far as fear is there in your heart, happiness can not be perfect." — Thich Nhat Hanh

"Nirvana is not something you get in the future. Nirvana is the capacity of removing wrong notions, wrong perceptions—which is the practice of freedom. Nirvana can be translated as freedom....When you get in touch with reality you no longer have views—you have wisdom and a direct encounter with reality." — Thich Nhat Hanh