in context of this blog:
Force consists of units.
If we have more units of a given type than enemy we can attempt to equivalize (amount of) enemy units by preparing/arming equal amount of units with weapons meant to counter that force, and have rest of forces use mixed weapons, partly against that type of units, partly against other target(-s).
That way we have countering force with equivalent firepower and more supporting force(-s).
Countering units are specialized fully against given target.
Support units are not specialized fully against given target.
How easily unit defeats another (% of engagements succesfull) in a given conditions can be called efficiency against an unit in a given conditions.
If we have units that can defeat n of units of a given type 'easily' (efficiency of at least 90% of engagements), we can counter enemy force of m units with m/n units of such type of our own.
That way we can reach 'countering equivalence' against given force with m/n units of given type.
Efficiency of at least 90% we can call 'countering'.
Efficiency of more than 50% we can call 'superior'.
Efficiency of 50% we can call 'equivalent'.
Efficiency of less than 50% we can call 'inferior'.
Efficiency of less than 10% we call 'neglible'.
If we do not have countering efficiency, we can combine multiple units into a force and statistically assess their efficiency against the given target.
See also: Hacking firepower and operatibility.