Serialized Only (Default)
Fields that Unity does not serialize are not shown in the inspector, except when explicitly exposed using attributes like ShowInInspector.
This is similar to how the default inspector works.
All Public
All public fields are shown in the inspector, regardless of whether or not Unity can serialize them, except when explicitly hidden with attributes like HideInInspector.
Non-public fields are not shown, except when explicitly exposed using attributes like ShowInInspector.
All Except Hidden
All public and non-public fields are shown in the inspector, except when explicitly hidden with attributes like HideInInspector.