Definition of "validity"

The state of being valid, authentic or genuine.  examples

State of having legal force.  examples

A quality of a measurement indicating the degree to which the measure reflects the underlying construct, that is, whether it measures what it purports to measure (see reliability).  examples

(Christianity, theology) The genuinity, as distinguished from the efficacity or the regularity, of a sacrament as a result of some formal dispositions being fulfilled.