Impermanence is one of the "Three Dharma Seals," or foundational markers of the Dharma. Depending on the lineage, the third Dharma Seal may be different, but we'll address that when we get to it. Impermanence is our first Dharma Seal, and it's what it sounds like. All phenomena are impermanent. Nothing at all, in reality, is permanent or static. All things arise, change, and pass away. Think of the common aphorism, "No man can step in the same river twice, for it is not the same river, and he is not the same man."

Non-self is our second Dharma Seal. It is the principle that nothing at all, in reality, possesses an independent, unchanging "self." All things are inter-dependent. The mind labors under the delusion of a static, unchanging "self," which is a delusion. I arise, change, then will eventually pass away. My thoughts, my sense perception; each facet of the Five Aggregates (we'll get to this sometime later,) which form my mind arise, change, and fade away. No matter how thoroughly I investigate my mind, I cannot find a permanent "me."

Literally "blowing out," or "extinguishing," Nirvana is the spiritual goal. It is the complete elimination of the three poisons which keep individuals trapped in the cycle of rebirth. Or, as I personally like to describe it, the cycle of death, birth, and re-death. It is the total cessation of suffering, and complete transcension of karma. It is not a heaven or higher realm one is reborn into.

Like I said earlier, depending on the tradition, the third Dharma Seal is either "Nirvana" or "Suffering" (aka Dukkha.) Like we learned in the First Noble Truth, Buddhists acknowledge that life is inherently unsatisfactory. Life contains suffering. Nothing in the conditioned world (conditioned here more-or-less meaning impermanent due to a vast network of causes and conditions) is able to grant me permanent fulfillment, no matter how hard I search.