Definition of "serum" [se•rum]

• The clear yellowish fluid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot. Also called blood serum. (noun)
• Blood serum from the tissues of immunized animals, containing antibodies and used to transfer immunity to another individual. (noun)
• Watery fluid from animal tissue, such as that found in edema. (noun)
• Whey. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "They made what they called a serum, which they put into a man's body and which killed the pantoblast germs without killing the man."
• "Fetal bovine serum is highly diluted and eventually removed from cells during the growth of vaccine viruses."
• "Fetal bovine serum is used in the manufacture of vaccines."