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Since as long as I have been doing cell culture, the word confluency is used to describe the % growth of cells or area covered by them. However, no dictionary that I have found uses this word. I was wondering if anyone could reliably state where the meaning comes from or how the association began, and truly what it means. I don't believe I can post this on another stack exchange because the word doesn't have even a resembling meaning in the dictionary. Cell culture is such an integral part of cell biology, medical research and biological manufacturing. And this term is an integral part of cell culture. I was surprised to be unable to reliably verify it's meaning.

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    $\begingroup$ This is entirely a guess, but confluence loosely means when things come together. Perhaps confluency is alluding to cells coming together. $\endgroup$ – canadianer Feb 23 '15 at 20:56
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    $\begingroup$ I think that's a fair and sensible guess. $\endgroup$ – rhill45 Feb 23 '15 at 20:58
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Besides the etymologic explanation that @aandreev gave, in cell culture this term is commonly used to describe the density of adherent cells and it is used as a measure of their proliferation. It is usually combined with an estimated (or counted) percentage, so 10% confluency means that 10% of the surface the dish or flask used is covered with cells, 100% means that it is entirely covered. The cells grow twodimensional on the surface of the flask in this case. The picture below (from here) illustrates different levels of confluency:

enter image description here

The level of confluency is important as the cells change their growth with changing densities. Low density cells (10-20%) usually grow slower than 50% confluent cells. If the plate is complete grown by cells, they tend to grow much slower again. This influences their genetic program, behaviour in experiments and transfections.

As @Roland pointed out it is important to say that confluency is not a hard measure, but rather an estimate of the cell density. Different people will get different estimations, but the trend should be the same.

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  • $\begingroup$ Chris thank you thorough answer, any thoughts on the etymology of the word as used here other than @aandreev above? $\endgroup$ – rhill45 Feb 23 '15 at 22:26
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    $\begingroup$ @rhill45 Confluence means coming together. It actually does not mean how dense the culture is but this word has been used for several ages now for what Chris has said in his answer. Perhaps this term came from Dictyostelium (this is a wild wild guess) $\endgroup$ – WYSIWYG Feb 24 '15 at 4:48
  • $\begingroup$ @rhill45 I think aandreev's answer about the etymology is right. I don't know any other. $\endgroup$ – Chris Feb 24 '15 at 8:40
  • $\begingroup$ This is good answer. I would add though that the % confluence (area covered) is actually pretty hard to estimate by eye, since cultured cells often change size and conformation as they grow more dense. Different people typically give different estimates from the same image (I'm not sure that last one is 90%, for example :) So confluency numbers are rather unreliable. $\endgroup$ – Roland Apr 4 '16 at 5:54
  • $\begingroup$ @Roland Thanks, this is a good point. I will add it. $\endgroup$ – Chris Apr 4 '16 at 10:12
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con- (com-) is prefix that usually means "togetherness", joining. Root fluency/fluent comes from latin fluere, to flow.

Source: Google's definitions for con- and fluency. Google, probably, takes information from Merriam-Webster dictionary.

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