A transcendent state in which there is neither suffering, desire, nor sense of self, and the subject is released from the effects of karma and samsara. It represents the final goal of Buddhism. Relinquishing what you once considered significant, be it your desires or your accomplishments. In essence, setting free from restrictions be it, social, political or personal. It involves detaching oneself from all attachments and attaining a heightened state. This ultimate state is the state of highest happiness. Though it may sound contradictory, juxtaposing detachment and happiness, it is the bottom line, because it focuses on your innerself and requires you to free yourself from all the temporal fleeting bouts of happiness or so called desires to attain a true sense of fulfillment. All this sounds deep when you just glance at it, but in reality, it is simple and yet a profound learning.
A simple Wikipedia definition, puts the whole concept into picture –
Nirvana is an ancient Sanskrit term used in Indian religions to describe the profound peace of mind that is acquired with moksha (liberation). In shramanic thought, it is the state of being free from suffering. In Hindu philosophy, it is union with the Brahman (Supreme Being). The word literally means “blown out” (as in a candle) and refers, in the Buddhist context, to the imperturbable stillness of mind after the fires of desire, aversion, and delusion have been finally extinguished.
We all have our own dispositions, which are preformed notions, biases, opinions all which form our belief system, which defines our personality and character. These life influencing elements are imposed upon us often externally, many a times without consideration. Our most important life phases are affected by them and our critical decisions are based on them. They may or may not be wrong just as they may or may not pose a harmful outcome in the future.
So, basically abandoning things that matter, to understand your true self and identify things that should matter. After all that is happiness, a state of mind not contingent upon anything.