Avidity

In proteins, avidity is a term use to describe the combined strength of multiple bond interactions. Avidity is distinct from affinity, which is a term used to describe the strength of a single bond. As such, avidity is the combined synergistic strength of bond affinities rather than the sum of bonds.

It is commonly applied to antibody interaction
Where multiple, weak, non-covalent bonds form between antigen and antibody. Individually, each bond is quite readily broken, however when many are present at the same time the overall effect results in synergistic, strong binding of antigen to antibody.

If the clustered proteins form a matrix, such as a clathrin-coat, the interaction is described by the term matricity.