Sunyata can be thought of as the ultimate
negation, the ultimate
voidness. It should be made clear, however, that it is not simply
nothingness, for that would, in its own way, be a
thing, a particular and definite
state of being. Instead it is characterized by an absense of attachment to such particulars, going beyond them to the ultimate baselessness of reality. And that is they key- that there is no
fundamental basis of reality.
Early scholastic Mahayana Buddhism was quite fond of distilling wisdom into fairly brief essays, generally in Sanskrit or Pali with names like The Perfection of Insight in 8000 Verses. The most succinct of these expresses The Perfection of Insight in One Letter: A. As in all other Indo-European languages, "a" here is the prefix meaning "not". That is, the ultimate insight is to gain a state of mind free from attachment and preconception, to achieve an understanding of sunyata.