Definition of common essential genes

In the web portal, common essential genes are defined as: A gene which, in a large, pan-cancer screen, ranks in the top X most depleting genes in at least 90% of cell lines. X is chosen empirically using the minimum of the distribution of gene ranks in their 90th percentile least depleting lines.

Could someone help clarify what it means by “minimum of the distribution of gene ranks in their 90th percentile least depleting lines”?

Thank you!!!