<Stats>
      <EffectType>ManufacturingCost</EffectType>
      <Scope>Global</Scope>
      <Target>
        <TargetType>Improvement</TargetType>
        <ImprovementType>Manufacturing</ImprovementType>
      </Target>
      <BonusType>Multiplier</BonusType>
      <Value>-0.05</Value>
    </Stats>
    <Stats>
      <EffectType>ManufacturingCost</EffectType>
      <Scope>Global</Scope>
      <Target>
        <TargetType>Improvement</TargetType>
        <ImprovementType>Research</ImprovementType>
      </Target>
      <BonusType>Multiplier</BonusType>
      <Value>-0.05</Value>
</Stats>

One is for manufacturing improvements, the other is for research improvements.

Could be stated more clearly ingame.

I think it's only monetary costs though?  It doesn't make it cheaper to construct with production points, or at least it sure doesn't show that it does?

I always assumed that ManufacturingCost applied to Rush buying only (From reading stuff here on the forums/steam forums). But, after going over the code and a few tests, it applies to both Rush buying and Construction cost. I also have to agree with zuPloed, ingame tooltips for improvements do not seem to get updated with adjustments, they can also be quite misleading due to the fact they do not specify the target of said adjustments. You can for example add a modifier to an improvement, trait or ability that adds say a 50% increase to asteroid mining or faction wide bonus and both display the same in tooltips, +50% Raw Production. They should display the target too: +50% Raw Production (Asteroids) or +50% Raw Production (Faction).