  The three-point correlation function (3PCF) of the 21cm brightness
temperature from the Epoch of Reionization (EoR) probes complementary
information to the commonly studied two-point correlation function (2PCF) about
the morphology of ionized regions. We investigate the 21cm 2PCF and 3PCF in
configuration space using semi-numerical simulations and test whether they can
be described by the local quadratic bias model. We find that fits of bias model
predictions for the 2PCF and 3PCF deviate from our measurements by $\sim 20\%$
at scales above the typical size of ionized regions ($\simeq 30$ Mpc) and at
early times with global neutral fractions of $\langle x_{\rm HI} \rangle
\gtrsim 0.7$. At later times and smaller scales these deviations increase
strongly, indicating a break down of the bias model. The 2PCF and 3PCF fits of
the linear bias parameter agree at the $10\%$ level for different EoR model
configurations. This agreement holds, when adding redshift space distortions to
the simulations. The relation between spatial fluctuations in the matter
density and the 21cm signal, as predicted by the bias model, is consistent with
direct measurements of this relation in simulations for large smoothing scales
($\gtrsim 30$ Mpc). From this latter test we conclude that negative amplitudes
of the 21cm 3PCF result from negative bias parameters, which describe the
anti-correlation between the matter over-densities and the 21cm signal during
the EoR. However, a more detailed interpretation of the bias parameters may
require a description of non-local contributions to the bias model.
