In cell culture, the term “confluent” refers to the state when cells have grown and spread across the entire surface of a culture vessel, forming a continuous monolayer with no or very little empty space between the cells. Confluence is an important aspect of cell culture as it influences cell behavior, morphology, and response to various treatments or experimental conditions.

When cells reach confluence, they typically exhibit contact inhibition, which is a regulatory mechanism that slows down or stops cell division when cells come into contact with each other. This mechanism helps maintain proper cell density and prevents overcrowding in the culture. However, some transformed or cancerous cell lines may not exhibit contact inhibition and can continue to divide and pile on top of each other, forming multilayers or clusters.

It is essential to monitor the confluence of cultured cells, as it helps determine when to passage or subculture the cells to maintain healthy growth and prevent over-confluence, which can negatively impact cell viability and function. Depending on the cell line and experimental goals, cells may be passaged when they reach a specific confluence level, typically around 70-90% confluence for adherent cells.