(general) The act of clumping together or adhesion of particles.
(biology) The clumping together of cells (such as bacteria and red blood cells) or particles.
Biological agglutination occurs in (but not limited to) the following instances: (1) clumping of cells in response to an antibody, (2) the adhesion of small particles that are suspended in a solution, which are then (usually) precipitated (3) in allergic reactions, when cells clump together to prevent antigens from entering.
Word origin: from the Latin agglutinare, meaning “to glue to”
Related forms: agglutinin (noun), agglutinate (verb).
Related terms: cross agglutination, direct agglutination, false agglutination, group agglutination, indirect agglutination, mixed agglutination, passive agglutination, spontaneous agglutination.