in vitro in vi·tro (ĭn vē'trō)
In an artificial environment outside a living organism.
In an artificial environment, such as a test tube. Compare in vivo.
In the laboratory; literally, “in glass” (laboratory experiments are often carried out in glass containers). In vitro conditions are distinguished from conditions that actually apply in nature. (Compare in vivo.)
Note: In vitro appears in the expression in vitro fertilization, a way of producing human embryos in a laboratory.