Purity is the state of being pure; the opposite of purity is impurity.
Purity may refer to:

Morality, the concept of human ethics
Black Oil virus, codenamed Purity in The X-files
Purity Supermarkets, a brand formerly used for a supermarket chain by Woolworths Limited in Tasmania, Australia
Purity Distilling Company, the company responsible for the Boston molasses disaster
"Purity", a song by the band Slipknot on their self-titled album Slipknot