- (Britain, Ireland, informal) an immersion heater
- the total submerging of a person in water as an act of baptism
- (astronomy) The disappearance of a celestial body, by passing either behind another, as in the occultation of a star, or into its shadow, as in the eclipse of a satellite; opposed to emersion.
- the act of immersing or the condition of being immersed
- (mathematics) a smooth map whose differential is everywhere injective, related to the mathematical concept of an embedding