By default, it usually means effective porosity which measures the true void containing the hydrodynamically connected fluids (also called free fluids) within each pore element.
The other meanings are:
All the above provide the various assessment of the porosity development with account for logging tool specifics.
See also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics (PP) / Volumetric Rock Model
[ Basic reservoir properties ] [ Pore volume ] [ Open pore volume ] [ Closed pore volume ] [ Porosity ] [ Open porosity ] [ Closed porosity ] [ Effective porosity (PHIE) ]