polyclonal antobody is the antibody produced for many or non specific antigens but antiserum is the antibody for a specific antigen

Polyclonal antibody

Polyclonal antibodies showed up in the blood test.
Rabbits are the most common animal for polyclonal antibody production.
Chickens are sometimes used for polyclonal antibody production.

Polyclonal antibody recognizes several epitopes on the target protein while monoclonal antibody recognizes only single epitope, hence monoclonal antibodies are more specific than polyclonal antibodies. However, sometimes MAbs are not able to precipitate the antigen because the epitope might need to be exposed on the surface of the antigen to be recognized by the antibody. Since some of the epitope might be hidden and it's a single epitope that is recognized by the monoclonal antibody, the propability of the antibody to reconize the epitope is lower compared with the polyclonal antibody that recognizes several epitopes on the target protein this is the reason for the tendency of polyclonal antibodies to have cross-reaction as compared to MAbs. by Victor S Gruezo Jr

Polyclonal antibody recognizes several epitopes on the target protein while monoclonal antibody recognizes only single epitope. Sometimes, monoclonal antibodies are not able to precipitate the antigen because the epitope might need to be exposed on the surface of the antigen to be recognized by the antibody. Since the epitope might be hidden and it's a single epitope that is recognized by the monoclonal antibody, the propability of the antibody to reconize the epitope is lower compared with the polyclonal antibody that recognizes several epitopes on the target protein.