When Cisco realizes he and Chester are stuck in Masonville in the past, trapped within the city by an invisible barrier, he says they've been "Under the Domed"; referencing the Stephen King novel Under the Dome, and the TV series of the same name; which is based on the book.
Each member of Team Flash has their clothing changed to a different era as the Still Force time bubble gets more chaotic. Joe - 1930s, Caitlin - 1980s, Frost - 1960s, Iris - 1970s.
The costumed Flash doesn't appear in this episode.
Frost mentions Norvock brought her stuff out of storage for her, revealing their friendship is still intact post-Crisis.
This is the second Arrowverse episode to use the title format from Friends in the name of the episode. The first was The One Where We're Trapped on TV (2020).