The absence of motile spermatozoa in semen.
Azoospermia may be caused by a defect in spermatogenesis or by a physical obstruction that hinders the sperm to be mixed with the rest of the ejaculatory fluid.
Word origin: a-, without + -zoo- » Greek zôion, animal + -spermia.
Compare: oligozoospermia, polyspermia.
See also: sperm count.