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  1. In spaceflight, injection is: (a) The process of putting an artificial satellite into orbit. (b) The time of such action.

    Injection altitude is the height at which a space vehicle is turned from its launch trajectory into an orbital trajectory. Injection mass is the mass of a space vehicle at the termination of one phase of a mission which continues into the next phase.

  2. In mathematics, an injection is a one-to-one mapping.

  3. In medicine, an injection is the use of a syringe and needle to introduce drugs or other fluids into the body to diagnose, treat, or prevent disease. Most injections are either intravenous (into a vein), intramuscular (into a muscle), or intradermal (into to the skin).