An ovum is the female gamete. In an anisogamy system it is the larger gamete type, generally contributing substantial cytoplasm as well as a genetic contribution to the zygote.
An oocyte is a developing female germ biological cell; its stage of meiosis matters when describing the gamete precisely. Oogenesis often partitions most of the cytoplasm into one large product while small polar bodies receive the other chromosome complements.
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