The LC50 calculation is a type of bioassay that measures toxicity. The LC50 is the required concentration of a toxin that would kill 50 percent of the population. The LC50 is also referred to as the lethal concentration 50 or the median lethal concentration.
According to the American Heritage Stedman's Medical Dictionary, a bioassay is a test used to determine the strength or activity of a substance. In the case of the LC50 bioassay, the measurement is the median concentration that will prove fatal to half the population of the test subjects in a single episode of exposure. The lower the lethal concentration, the more toxic the chemical. LC50 bioassays are specific to species and conditions, such as length of time from exposure until death. The results of an LC50 for one species does not transfer to another and cannot be extrapolated to humans.