In vitro (Latin for (with)in glass) means within a test tube, or just outside a living organism (a cell). An example is In Vitro Fertilization. The opposite of in vitro is in vivo, within a cell. As many experiments that deal with molecular biology are conducted outside of cells, and the conditions do not necessarily represent the conditions inside the cell, results are often annotated with in vivo or in vitro.
... later that evening, Kitty rejects him in the expectation that Vronsky is about to propose to her.
The following morning Stiva and Vronsky are at the station to welcome ...