oocyte vs egg
An oocyte is an immature egg cell. The oocyte will eventually break free from the follicle and travel down the fallopian tube – at which point it's called an egg (or ovum, if you're that way inclined). Once the egg gets fertilised by the sperm, it's a zygote.[1]
A developing egg is called an oocyte. Its differentiation into a mature egg (or ovum) involves a series of changes whose timing is geared to the steps of meiosis in which the germ cells go through their two final, highly specialized divisions.[2]