OD600

OD600 is an acronym indicating the optical density of a sample measured at a wavelength of 600 nm. Also written as "O.D. 600," "o.d. 600," etc. It is a common method for estimating the concentration of bacterial or other cells in a liquid.

Concentration tells the stage of cultured cell population. The stage of population tells if the population is in exponential growth phase or lagging phase. Value of concentration depends on used culturing medium.