What is the river of forgetfulness in the underworld?

In mythology, particularly in Greek mythology, the river of forgetfulness is known as Lethe. It is one of the five rivers of the underworld and is said to flow through Hades. Souls who drink from Lethe forget their earthly lives and experiences, which allows them to be reborn without memories of their past. The river symbolizes the theme of forgetfulness and the cycle of life and death.