In true Existentialist fashion, there is not one exact and precise overarching definition of Existentialism's meaning.  I believe that part of the meaning of Existentialism is the absence of a structure that determines human essence.  The dictum of "existence precedes essence" is of utmost importance here.  The meaning of Existentialism is rooted in the idea that human experience is defined by human experience.  There is not a transcendent or totalizing force that determines being.  The implications here is that human freedom is what constructs the essence of consciousness.  The meaning of Existentialism becomes one in which individuals recognize that they are on their own, absent of a transcendent force or figure that governs being.  Another part of the meaning of Existentialism is one of constant resistance against attempts of "bad faith" to insert a totalizing force in order to avoid human responsibility for the making of choices.  The agonizing notion of freedom and the ability to have to make such choices and decisions becomes the essence of human existence.  The meaning of Existentialism is one that vaults this element into the forefront of being and lies at the heart of human consciousness.  It also lies at the heart of Existentialism's meaning.