An active fault is a fault that has displayed recent seismic
activity, while an inactive fault has not displayed recent seismic activity.
There really is no way to concretely define a fault as "active" or
"inactive" (especially because inactive faults can suddenly become
active again), but it's more or less safe to say that if a fault hasn't shown
tectonic activity for about 5,600 years, it's probably
inactive.
See attached file for the list of inactive faults and volcanoes in the Philippines.
