Biofluid: A biological fluid. Biofluids can be excreted (such as urine or sweat), secreted (such as breast milk or bile), obtained with a needle (such as blood or cerebrospinal fluid), or develop as a result of a pathological process (such as (such as blister or cyst fluid). The term biofluid is employed as both a noun (as in the aforementionned biofluids) and an adjective (as in biofluid dynamics and biofluid mechanics).