Dreamworld was the Candy Crush Saga mode that used a separate set of lives from the main game.
Dreamworld was introduced as an alternate game world featuring the owl Odus. Players could switch between regular Candy Crush Saga levels and Dreamworld without sharing the same life supply, making it possible to continue playing in one mode after running out of lives in the other.
Dreamworld also changed the gameplay. Players had to keep candies of two colors balanced on a scale while making matches. Filling a meter triggered the Moon Struck power, which cleared candies of those colors and temporarily altered the board.
A common mix-up is treating Dreamworld as a separate Candy Crush title. It was actually an alternate mode within Candy Crush Saga, and it was later removed, so it is no longer accessible in the current game.