The Multiverse as depicted in Smallville.
Crisis was an interdimensional event, caused by the Monitors, where they set out to destroy all universes in the Multiverse.
Season Eleven[]
Desiring to end all existence, the Monitors began wiping out universes with Earth-2, Earth-9, Earth-13, Earth-37 and Earth-Majestic all being destroyed. However, when the Monitors came to Earth-1, Lex Luthor managed to convince the Monitors to "reboot" Earth-1, rather than razing it. Using blue Bleed, the Monitors began to break down and collect everything on Earth-1. Superheroes, led by Superman, joined forces to fight back against the Monitors. When Superman was hit by the blue Bleed, his entire history began to fall apart, but his willpower proved too strong for the blue Bleed. Superman was able to will himself back into existence, while Red Tornado hacked into and took control over the Monitors' ships, using them to restore the universe. However, anyone who had died remained dead. The Monitors were locked away by the Justice League.
In the Comics[]
There have been many Crisis events in DC Comics.
The most famous being Crisis on Infinite Earths (1985-1986). In the storyline, the Anti-Monitor (the Monitor of the Anti-Matter universe) sets out to wipe out all universes. The superheroes of many universes joined forces to combat him. The event led to the deaths of Supergirl and the Flash (Barry Allen), along with the destruction of the Multiverse. Five Earths survived and combined into one single Earth, known as New Earth.
1994, DC Comics released Zero Hour: Crisis in Time!. It revolved around Hal Jordan (then Parallax) attempting to destroy and then re-create the DC universe. The superheroes of New Earth managed to stop him, with them recreating a slightly different universe, with minor differences.
In 2005 came Infinite Crisis, which saw the return of surviving pre-Crisis on Infinite Earths Superman and Lois Lane of Earth-Two and Superboy-Prime. The event caused the creation of a new Multiverse, with 52 universes rather than infinite.