The Polyakov loop in the fundamental representation has been used repeatedly as an order parameter in the deconfinement phase transition. I will describe results [1] for the confinement-deconfinement phase transition as predicted by the Nambu--Jona-Lasinio model where the local and quantum Polyakov loop is coupled to the constituent quarks in a minimal way (PNJL). We observe that the leading correlation of two Polyakov loops describes the chiral transition accurately [2]. On the other hand, using quite general chiral quark models of QCD featuring spontaneous chiral symmetry breaking and implementing the quantum and local nature of the Polyakov loop [1,3], we argue that, in the confined phase, its expectation value can be represented in terms of hadrons with exactly one heavy quark, similarly to the hadron resonance gas model for the pressure [4,5,6]. We derive an approximate sum rule that gives a fair description of available lattice data with N_f = 2+1 for temperatures in the range 150 MeV