What exactly is a passage?

[guidedgateway]

I have some bio homework and it asks a question about different passages, like passage 1 passage 2 and so on. I was actually wondering what a passage was. If anyone could help out that would be great.

[stern_daniel]

Hi,
it's quite simple: your cells in your cell culture flask can only grow until they are adjacent to each other (at this point, contact inhibition prohibits further growth in cell lines and your cells would stop growing or even die). If this point is reached, you'd have to harvest your cells either by scraping them off the vessel or by adding Trypsin (which helps to loosen the contact of the cells to the plastic surface of the vessel) and dilute them in fresh medium, so that they can grow again.
This procedure is called a passage!
Hope I could help you a little

Daniel