Name is indeed not very descriptive...
Let's start with a docstring, smth like

"""Config reader for files with options grouped in [Definition] and [Init] sections

Is a base class for readers of filters and actions, where definitions in jails might
provide custom values for options defined in [Init] section
"""

So I guess the class name could be smth like "StructuredConfigReader"? or "DefinitionInitConfigReader" ;-)  but something along those lines with somewhat descriptive name, may be?