noun

• The act of immersing or the condition of being immersed.
• The total submerging of a person in water as an act of baptism.
• Deep engagement in something.
• (Britain, Ireland, informal) An immersion heater.
• (mathematics) A smooth map whose differential is everywhere injective, related to the mathematical concept of an embedding.
• (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.
• (education) A form of foreign-language teaching where the language is used intensively to teach other subjects to a student.
• One's suspension of disbelief while reading, playing a video game, etc. The experience of losing oneself in a fictional world.