We present a theoretical discussion of the reversible parking problem, whic
h appears to be one of the simplest systems exhibiting glassy behavior. The
existence of slow relaxation, nontrivial fluctuations, and an annealing ef
fect can all be understood by recognizing that two different time scales an
present in the problem. One of these scales corresponds to the fast fillin
g of existing voids, the other is associated with collective processes that
overcome partial ergodicity breaking. The results of the theory are in a g
ood agreement with simulation data; they provide a simple qualitative pictu
re for understanding recent granular compaction experiments and other glass
y systems. [S1063-651X(99)14402-7].