oocyte vs. ovum

oocyte

noun

Cell Biology.
  1. an immature egg cell of the animal ovary; in humans, one oocyte matures during the menstrual cycle, becoming an ootid and then an ovum, while several others partially mature and then disintegrate.

ovum

noun

plural ova
  1. Cell Biology.
    1. the female reproductive cell or gamete of animals, which is capable of developing, usually only after fertilization, into a new individual.
    2. the female reproductive cell or gamete of plants.
  2. Architecture. an oval ornament, as in an egg-and-dart molding.