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(2n), a nonperturbative generalization A(Q(2)) of the perturbative QCD running coupling a(Q(2)) (equivalent to alpha(s)(Q(2))/pi). Recent large volume lattice calculations for these dressing functions indicate that the coupling defined in such a way goes to zero as A(Q(2)) similar to Q(2) when the squared momenta Q(2) go to zero (Q(2) << 1 GeV2). In this work we construct such a QCD coupling A(Q(2)) which fulfills also various other physically motivated conditions. At high momenta it becomes the underlying perturbative coupling alpha(Q(2)) to a very high precision. And at intermediate low squared momenta Q(2) similar to 1 GeV2 it gives results consistent with the data of the semihadronic tau 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 A(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 tau-decay V + A spectral functions allows us to obtain values for the gluon (dimension4) condensate and the dimension-6 condensate, which reproduce the measured OPAL and ALEPH data to a significantly better precision than the perturbative (MS) over bar coupling approach.