In cell culture biology, confluence refers to the percentage of the surface of a culture dish that is covered by adherent cells.
For example, 50 percent confluence means roughly half of the surface is covered, while 100 percent confluence means the surface is completely covered by the cells, and no more room is left for the cells to grow as a monolayer.
Many cell lines exhibit differences in growth rate or gene expression depending on the degree of confluence.
Cells are typically passaged before becoming fully confluent in order to maintain their proliferation phenotype.
[2] Comparing the amount of space covered by cells with unoccupied space using the naked eye can provide a rough estimate of confluency.