The phrase "egg precursor" refers to something that comes before an egg forms. It is the early stage of an egg or the cell that has the potential to develop into an egg. Full definition
But many scientists doubt that egg precursor cells actually exist. (sciencemag.org)
By contrast, in a female, egg precursor cells divide only 24 times, all but one of these divisions occurring before she is born. (schizophrenia.com)
The tissue taken from the ovary is processed to yield stem cells called egg precursor cells, which have the potential to become eggs under the right conditions, Tilly says. (businessinsider.com)