  We propose a clear definition of the gluon condensate within the
large-$\beta_0$ approximation as an attempt toward a systematic argument on the
gluon condensate. We define the gluon condensate such that it is free from a
renormalon uncertainty, consistent with the renormalization scale independence
of each term of the operator product expansion (OPE), and an identical object
irrespective of observables. The renormalon uncertainty of
$\mathcal{O}(\Lambda^4)$, which renders the gluon condensate ambiguous, is
separated from a perturbative calculation by using a recently suggested
analytic formulation. The renormalon uncertainty is absorbed into the gluon
condensate in the OPE, which makes the gluon condensate free from the
renormalon uncertainty. As a result, we can define the OPE in a renormalon-free
way. Based on this renormalon-free OPE formula, we discuss numerical extraction
of the gluon condensate using the lattice data of the energy density operator
defined by the Yang--Mills gradient flow.
