Dagobah is both a planet and the system in which it resides, in the fictional Star Wars universe. It appears in the films The Empire Strikes Back and Return of the Jedi.
Dagobah, in the Sluis sector, is a world of murky swamps, steaming bayous, and petrified gnarltree forests. The ubiquitious white spiders that roam the swamps are actually newly sprouted seedlings of the gnarltrees that will take root and grow.
After Darth Vader hunted down nearly all of the Jedi, Jedi Master Yoda hid in a swamp on Dagobah where a cave strong with the dark side of the Force hid him from detection by the Emperor. In The Empire Strikes Back, Luke Skywalker is visited on the ice planet Hoth by the ghost of Ben Kenobi, who tells him to go seek Yoda on Dagobah to be trained as a Jedi. Skywalker flies to Dagobah with R2-D2 in his X-wing after Darth Vader and his stormtroopers overran the Rebel Alliance base on Hoth. Skywalker leaves Dagobah early to attempt to rescue Han Solo, Princess Leia, and Chewbacca who he feels are in danger on the planet Bespin. Skywalker also briefly returns to Dagobah in Return of the Jedi, in which he has a final conversation with Yoda, and speaks extensively to Obi Wan Kenobi's ghost about the conflicting stories of Luke's parentage.
It may be revealed in Revenge of the Sith how Yoda escaped from the Emperor and if Luke and Leia had been there before. Luke sensed a familiarity with the planet in Empire.
Dagobah appears to be a harsh, humid environment, mostly covered in water. Given director George Lucas's penchant for portraying planets as a single environment, we can assume that the swampy marshland that surrounds Yoda's hut is indicative of the entire planet.
In the expanded universe, Yoda confronted a Bpfasshi Dark Jedi on Dagobah some years before the events in The Empire Strikes Back. Eventually Yoda defeated the Dark Jedi, who died on Dagobah. The cave where the Dark Jedi died became strong in the dark side of the Force, and Yoda used this spot to hide from the Emperor and Vader.
The word Dagobah comes from a kind of Buddhist Shrine.
