This document discusses the prozone phenomenon, serial dilution, titer, and titration. The prozone phenomenon occurs when there is too much antibody present, blocking the reaction. Serial dilution is used to solve this by diluting the sample until the reaction occurs. Titer refers to the reciprocal of the last dilution tube that shows a positive reaction, and is a measure of antibody concentration or antigen expression level. Titration is a semi-quantitative method used to determine these values through serial dilution and observing the reaction.