Hypospermia
Hypospermia is a condition in which a man has an unusually low ejaculate (or semen) volume, less than 1.5 ml. It is the logical opposite of hyperspermia. It should not be confused with oligospermia, which means low sperm count.
Normal ejaculate when a man is not drained from prior sex and is suitably aroused, is around 1.5-6 ml, although this varies greatly with mood, physical condition and sexual activity. Of this, around 1% by volume is sperm cells. Hypospermia would only usually be a factor in infertility if the two conditions (hypospermia and oligospermia) are combined. The U.S. based National Institutes of Health defines hypospermia as a semen volume lower than 2 mL on at least two semen analyses.