Golden age

A golden age was an era or epoch regarded as superlative for some reason, though generally nostalgic ones. The general term was used on several occasions.

In-universe

 * Operation Golden Age, a plan to return Earth to a pre-industrial age (DW: Invasion of the Dinosaurs)
 * Britain's Golden Age, an aborted timeline in which Harriet Jones had a long and successful reign as prime minister (DW: World War III)

Out of universe

 * Golden Age (audio story), a Torchwood radio drama