A dream is a location or map. Dream areas are subdivisions of maps that can be unlocked. Individual dreams are grouped together into dream landscapes.
A player can reach their dreams via the respective travel structures (Wanderer's Hut, Sleigh, etc), or via the map button at the right side of the screen.
When visiting friends, their opened dreams are displayed as icons at the bottom of the screen. They are locked until the player has themselves opened the dream for themselves, allowing them to travel to their friend's same dream.