Definition of "observable" in English

adjective

1. Able to be observed.

   • The strange new star was at the edge of the observable universe.

2. Deserving to be observed; worth regarding; remarkable.

noun

1. (physics) Any physical property that can be observed and measured directly and not derived from other properties

   • Temperature is an observable but entropy is derived.
   • In quantum mechanics, observables correspond to Hermitian operators. Also, they act a lot like random variables. Taking their expected value one may recover something resembling a classical observable.