Default Mode Network
The DMN is the parts of the brain that are active when a person is not actively engaged in a task or is daydreaming. The DMN turns off when a person is focused on a particular task, but turns on again when resting or daydreaming.
In this case, the term “network” refers to a several regions in the brain being active and connected simultaneously.
The DMN is believed to be a source of creativity. The idea of having your best ideas in the shower stems from this.