1.NounThe act of inserting, or something inserted.
"The surgeon performed the insertion of a pacemaker.; The insertion of new text changed the meaning of the document.; The book contained the insertion of several illustrations."
2.NounThe distal end of attachment of a muscle to a bone that will be moved by the muscle.
3.NounThe addition of a nucleotide to a chromosome by mutation.
4.NounThe process of going from subcritical to prompt critical.