- The act of injecting, or something that is injected.
- (context, specifically, medicine) Something injected subcutaneously, intravenously, or intramuscularly by use of a syringe and a needle.
- (math) A function of "one-to-many" mapping relationship; more formally, f: X → Y is an injection if and only if, for every x in the function domain, domain X, there is at least one y in the function codomain, codomain Y with f(x) = y.
- the act of inserting, or something inserted
- (anatomy) the point of attachment of a muscle to a bone
- (genetics) the addition of a nucleotide to a chromosome by mutation