For parameter values PENDING means "unknown" and "not (yet) fixed".
Realise that "unknown" or "not (yet) fixed" means something completely different than "not available" or "0". A pending value is part of a model but not yet determined. A parameter with the values 0 really has 0 as its value (zero is not nothing...). When a parameter is not part of a model, it will not be available.
Note that Quaestor assigns the value -999999 to parameters with a pending value.
For CONSTRAINTs pending means that no sufficient data are available to evaluate either a DETERMINED TRUE or FALSE, implying that the decision to either reject or accept a particular relation in the template may need to be postponed until sufficient data are gathered.