A healing factor is a term used to describe the ability to recover from bodily injuries or disease at a superhuman rate.
The efficiency of a character's healing factor, as with all "powers", varies hugely depending on the situation and the writer writing it, with, as a story is being told, drama being the key factor.
Broad displays of artistic license have often led to debates among fans of particular comic book characters that have superhuman rates of healing, as to which comic characters heal faster, or exactly which level their healing factors are.
There are numerous characters within the Image Comics universe that possess some form of accelerated healing ability. The source of these "healing factors" ranges from genetic mutation to artificial enhancement to magic. The exact limits of each character's healing powers is often a source of debate among fans since that many of their healing powers have fluctuated in efficiency, due to the practice of artistic license by multiple writers and artists.
The members of the various groups and races possess their "healing factors" as a result of mystical energies and influences that are common to their species. Many members of the various "gods" are able to heal themselves by purposely channeling the mystical energies of their bodies to heal themselves to exceptional degrees.
However, some individual members of the groups and races possess near-true immortality, which means that they have completely stopped aging and they can't physically die except under specific circumstances. Some individual "gods" can only truly die if a significant portion of their bodily molecules are scattered, thus preventing them from regenerating vital areas of their anatomy essential to survival.