  Weakly Interacting Massive Particles (WIMPs) are among the best-motivated
dark matter candidates. In the standard scenario where the freeze-out occurs
well after the end of inflationary reheating, they are in tension with the
severe experimental constraints. Here, we investigate the thermal freeze-out of
WIMPs occurring {\it during} reheating, while the inflaton $\phi$ coherently
oscillates in a generic potential $\propto \phi^n$. Depending on the value of
$n$ and the spin of the inflaton decaying products, the evolution of the
radiation and inflaton energy densities can show distinct features, therefore,
having a considerable impact on the freeze-out behavior of WIMPs. As a result
of the injection of entropy during reheating, the parameter space compatible
with the observed DM relic abundance is enlarged. In particular, the WIMP
thermally averaged annihilation cross-section can be several magnitudes lower
than that in the standard case. Finally, we discuss the current bounds from
dark matter indirect detection experiments, and explore future challenges and
opportunities.
