The product of the gluon dressing function and the square of the ghost dressing function in the Landau gauge can be regarded to represent, apart from the inverse power corrections 1 / Q 2 n , a nonperturbative generalization  ( Q 2 ) of the perturbative QCD running coupling a ( Q 2 ) ( ≡ α s ( Q 2 ) / π ). Recent large volume lattice calculations for these dressing functions indicate that the coupling defined in such a way goes to zero as  ( Q 2 ) ∼ Q 2 when the squared momenta Q ² go to zero ( Q 2 ≪ 1 GeV 2 ). In this work we construct such a QCD coupling  ( Q 2 ) which fulfills also various other physically motivated conditions. At high momenta it becomes the underlying perturbative coupling a ( Q 2 ) to a very high precision. And at intermediate low squared momenta Q 2 ∼ 1 GeV 2 it gives results consistent with the data of the semihadronic τ lepton decays as measured by OPAL and ALEPH. The coupling is constructed in a dispersive way, resulting as a byproduct in the holomorphic behavior of  ( Q 2 ) in the complex Q ² -plane which reflects the holomorphic behavior of the spacelike QCD observables. Application of the Borel sum rules to τ -decay V + A spectral functions allows us to obtain values for the gluon (dimension-4) condensate and the dimension-6 condensate, which reproduce the measured OPAL and ALEPH data to a significantly better precision than the perturbative MS ¯ coupling approach.