The Paper Age
Roughly, the period of comics between the late 1980s and the early 2000s. Also known as the Dark Age, protagonists during this period were usually dark anti-heroes or gritty reboots of established heroes. Power levels tended to be much the same as the Bronze Age.
An important aspect of the Iron Age was “realism”. Alan Moore’s Watchmen was a deconstruction of the superhero genre that explored what it would be like like if superheroes existed in the real world†. Now superheroes were emotionally ravaged by the crimes they witnessed or became every bit as violent and grim as the villains they fought.
†It’s worth noting that Alan Moore despised the trend of darkness in comics that Watchmen inspired, and followed it with a more upbeat, Silver-Age-y Tom Strong.