“Nibbana is serene” is the opposite to “All asavas are suffering”. The term Nibbana means no flux or no-defilement. Which is the elimination of the cause and effect of suffering, and the cessation of the Twelve Links of Dependent Origination. The Basis of Twelve Links is the principle of “When this exists, that exists. Because this comes into being, that comes into being.” The cessation of the twelve links follows from the principle from the principle. “If this does not exist, that does not exist, if this ceases, that ceases.” Sufferings of old age, death, worrying, and sorrow are dependent upon the condition of birth, so the cessation of birth can result in the cessation of the sufferings of old age, death, worrying and sorrow. Likewise, the cessation of desire, grasping and becoming the cessation of ignorance results in the cessation of mental formations or the cause of all bitter fruits. When the cessation of ignorance, mental formations, consciousness and so on finally result in the cessation of old age and death, then Nibbana has been attained. To be more explicit, as soon as the complete cessation of impure and defiled causes and conditions has been completed, ignorance will be turned into undefiled and pure wisdom, through which the truth and reality of all dhammas can be seen. This is Nibbana, which is also called Nibbana with corporalremainder. The meaning of Nibbana is perfect peach or tranquility, or an eternally happy and joyous state in which wisdom, happiness and virtue are perfectly achieved. Buddhists view this state as attainable only by holy ones, and thus can not be judged by experienced conceptions like existence, non-existence, coming and going. It is an inconceivable state of emancipation. As I mentioned above, Nibbana can be interpreted as passing away. Actually, Sakyamuni attained Nibbana and became a Buddha at the age of 30, yet his corporal body remained as the residential fruit of his former illusion and kamma. This is Nibbana with remainder. It was not until his death at the age of 80, that he entered Nibbana without remainder. (From Essentials of Buddhism: Questions and Answers)