According to Osho, nirvana is the total realization that what we call death does not exist and what we call life is also not true life. Knowing only deathlessness still binds you to rebirth through the desire to live. When both illusions are seen through, the identification with the body ends, desire ceases, and the cycle of return stops—nirvana.
Nirvana means seeing that death isn’t real and ordinary life is a mirage, so the urge to come back ends.