$300 CSL SOON., page-182

It refers to the maximum price people are willing to buy it for and the minimum price people are willing to sell it for when the market opens.
e.g. if someone has a buy order for 330, as long as the stock opens below 330 (e.g. open of 302) they will purchase it (at the open price of 302). Same with the sell order of 280, as long as it opens above 280 they will sell it (at the open price of 302).

ASX uses an algorithm with all these preopen buys and sells to determine the open price of the stock

This article helps explain it, I was wondering the same thing once i started investing 2 years ago.
https://rivkin.com.au/resources/understanding-the-asx-opening-and-closing-auctions/