1) Biological cell 2) Egg cell 3) Egg cell after meiosis 4) Ovum 
The nearly mature ovum after the first meiotic division has been completed and the second initiated; in most higher mammals, the second meiotic division is not completed unless fertilization occurs. ... Origin: G. Ootidion, a diminutive egg. See -id ... (05 Mar 2000) ... 
(o´o-tid) a mature oocyte; the cell produced by meiotic division of a secondary oocyte. In mammals, this second maturation division is not completed unless fertilization occurs.
Type: Term Pronunciation: ō′ō-tid Definitions: 1. The nearly mature oocyte after the first meiotic division has been completed and the second initiated; in most higher mammals, including humans, the second meiotic division is not completed unless fertilization occurs. Thereafter the ootid contains two separate haploid elements, the ...
In Zoology, an ootid is an immature female gamete that develops into an ovum.
[n] - mature ovum after penetration by sperm but before the formation of a zygote
noun mature ovum after penetration by sperm but before the formation of a zygote
the cell that results from the meiotic divisions of an oocyte and matures into an ovum.