In biology, "agglutination" can mean a couple of things:
- The clumping together of cells due to the binding of agglutinin (a protein) molecules on each cell's surface.
- The clumping together of two microbial organisms of the same species for the purpose of sexual reproduction. This is often conducted by means of a carbohydrate on one organism and a protein on the other, resulting in a glycoprotein (agglutinin) that helps helps them stick together.
From the science dictionary at http://biotech.icmb.utexas.edu/