"Quality is value to some person” - G. Weinberg. This is a common definition of quality in software testing. J. Bach and M. Bolton has the addendum "...who matters" which specifies more clearly that the person referred to should be a stakeholder of some kind.

"Quality is to a product what character is to a man" - Henry John Heinz

ISTQB: The degree to which a component or system satisfies the stated and implied needs of its various stakeholders.