Hybridoma (hybrid = mixture of two cells, "oma" is coming from cancer e.g a melanoma) cells are used for the production of commercial amounts of a single antibody by creating an cancerous plasma cell that continues to divide and divide. These antibodies have numerous commercial applications.

Here is an animation of monoclonal antibody production. The word "epitope" is another word for an antigen.

Monoclonal antibodies are used to test for the presence of HCG hormone which indicates pregnancy. This animation (listen to the narrated version) outlines the use of monoclonal antibodies in the pregnancy test kit.