serum vs body fluid

serum and body fluid both are nouns.

Word	Noun	Adjective	Verb	Adverb
serum	Yes	No	No	No
body fluid	Yes	No	No	No

As nouns, body fluid is a hypernym of serum; that is, body fluid is a word with a broader meaning than serum:

serum: an amber, watery fluid, rich in proteins, that separates out when blood coagulates
body fluid: the liquid parts of the body

Other hypernyms of serum include bodily fluid, humor, humour, liquid body substance.

serum (noun)	body fluid (noun)
an amber, watery fluid, rich in proteins, that separates out when blood coagulates	the liquid parts of the body