I will quote WikiPedia:
"The teaching on the emptiness of all phenomena is a core basis of Buddhist philosophy and has implications for epistemology and phenomenology. It also constitutes a metaphysical critique of Greek philosophical realism, Abrahamic monotheism and Hindu concept of atman. Moreover, contrary to widely misconceived equation to the doctrine of nihilism, grasping the doctrine of sunyata is seen as a step to liberation. Unlike nihilism, emptiness maintains the Buddha's purpose.
Śūnyatā signifies that everything one encounters in life is empty of absolute identity, permanence, or an in-dwelling 'self'. This is because everything is inter-related and mutually dependent - never wholly self-sufficient or independent. All things are in a state of constant flux where energy and information are forever flowing throughout the natural world giving rise to and themselves undergoing major transformations with the passage of time.
This teaching does not connote nihilism. In the English language the word emptiness suggests the absence of spiritual meaning or a personal feeling of alienation, but in Buddhism the realization of the emptiness of phenomena, at basic level, enables one to realise that the things which ultimately have no independent substance cannot be subject to any irreconcilable conflicts or antagonisms. Ultimately, true realisation of the doctrine can bring liberation from the limitations of form in the cycle of uncontrolled rebirth.
Rawson states that: "[o]ne potent metaphor for the Void, often used in Tibetan art, is the sky. As the sky is the emptiness that offers clouds to our perception, so the Void is the 'space' in which objects appear to us in response to our attachments and longings." The Japanese use of the Chinese character signifying Shunyata is also used to connote sky or air."