What is the reaction between antibody and particulate antigens called?

The reaction between antibody and particulate antigen is called agglutination.

Agglutination is the process by which particles suspended in a liquid are brought together and clump together, forming a visible aggregate. This reaction is most commonly observed when antibodies bind to antigens present on the surface of the particulate antigen, causing them to clump together. This process is the basis for many serological tests, such as the Widal test and the Wasserman test, which are used to diagnose various infectious diseases.