The oogonium becomes a primary oocyte, which begins the first meiotic division but is arrested in prophase I until puberty.

The process you're referring to is part of oogenesis, which is the creation of an ovum (egg cell) in females. Here's the step-by-step process:

1. Oogonia (plural of oogonium) are cells that divide mitotically to produce primary oocytes. This happens during the fetal development stage in females.

2. Each primary oocyte then begins the process of meiosis, which is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell. This is how genetic diversity is achieved.

3. However, the primary oocyte doesn't complete meiosis I immediately. It gets arrested in the prophase of meiosis I. This is a stage where the chromosomes condense and the meiotic spindle begins to form, but the cell doesn't proceed to the next stages of meiosis I.

4. This arrest continues until puberty. At puberty, each menstrual cycle typically allows for the completion of meiosis I for one primary oocyte, producing a secondary oocyte and a smaller polar body.

5. The secondary oocyte then begins meiosis II but is again arrested, this time in metaphase II. It will only complete meiosis II if fertilization occurs.

So, the statement you provided is referring to the early stages of oogenesis, where an oogonium becomes a primary oocyte and begins meiosis I, but doesn't complete it until puberty.