Avidity

Definition
noun, plural: avidities
The combined strength of bond affinities in a complex.
Usage
The term may be used in chemistry to describe the dissociation-dependent strength of an acid or base. In proteins, avidity describes the binding intensity of multiple bond interactions between proteins.
In immunology, avidity refers to the strength of antibody–antigen binding. In this regard, avidity may be different from affinity. The latter being a term used to describe the strength of a particular bond, i.e. the affinity of an antibody for the antigen as the strength of a non-covalent association between an antigen-binding site with a single antigenic epitope¹. For instance, IgM may have low affinity but it has high avidity due to its 10 weak binding sites contrary to the two strong binding sites of IgG.
Miscellaneous
Compare: affinity
See also: antibody-antigen complex, protein
Reference:
¹Mak, Tak W. and Mary E. Saunders. Primer to the Immune Response. Amsterdam: Academic/Elsevier, 2008. 74.