A morphological abnormality visible upon biopsy of the germinal epithelium of the testis in which the cellularity of the germinal epithelium is reduced in general, so that all stages of germ cells (spermatogonia, spermatocytes, and spermatids) are present but reduced in number. This term applies to biopsies with some tubules showing diminished amounts of qualitatively complete spermatogenesis in combination with a vast majority of tubules that lack germ cells. [from
HPO]