Agglutination(biology)

• Agglutination is the clumping of particles. The word agglutination comes from the Latin agglutinare, meaning "to glue to."
  This occurs in biology in three main examples:
  The clumping of cells such as bacteria or red blood cells in the presence of an antibody. The antibody or other molecule binds multiple particles and joins them, creating a large complex.
  The coalescing of small particles that are suspended in solution; these larger masses are then (usually) precipitated.
  An allergic reaction type occurrence where cells become more compacted together to prevent foreign materials entering them. This is usually the result of an antigen in the vicinity of the cells.