The Interregnum
The time between The Golden Age of Comic Books and The Silver Age of Comic Books. Superheroes were at their lowest ebb here; the end of World War II meant that people were tired of hearing about individuals fighting to save the world, and other genres of comic book took over -- horror, crime, Funny Animals, and so on.
By the end, only a few Superhero comics were still going, Batman, Superman, and Wonder Woman chief among them. Plastic Man was the last non-DC superhero left before being bought out. Apart from a few scattered and failed attempts at revivals such Atlas Comics' Captain America (which was later retconned in the 1970s as the adventures of an impostor soon driven insane by a flawed copy of Project: Rebirth) and Sub-Mariner while Jack Kirby and Joe Simon tried their disguised attempt with Fighting American and Stunt Man, the genre seemed to have no life in it. However, they did kickstart the romance comic genre with Young Romance, which proved a big success.
This was the era when the Comics Code was enacted, and it may have been what ultimately brought superheroes back. Though the hearings that led to it put some of the blame on superheroes, they were especially unkind to crime and horror, and those genres were pretty much gutted by the Code. Meanwhile, superheroes were easy enough to retool to follow the Code, and experienced a resurgence in popularity that led to The Silver Age of Comic Books.
The end of the age is pegged at different points, depending on who you talk to; the most common is the Revival of the Flash by DC Comics in 1956, but some say it happened before that, with the introduction of the Martian Manhunter in 1954, and some say it didn't happen until later, with the appearance of Marvel's Fantastic Four in 1961.
It is also sometimes referred to as the Atomic Age (because of the nuclear paranoia in the 1950's affecting comics). Opinions differ on whether it should be considered part of the Golden Age or whether it counts as a separate age.
The Interregnum of Super Hero Comics is not to be confused with The Interregnum of World Chess Champions, or George Grosz' Interregnum.