1. Transfer in farming and agricultural processing of a component from one system such as soil or feed to another system such as a plant, animal or human being: carry-over is expressed as the concentration of the component in the second system divided by its concentration in the first.

2. Process in analytical studies by which materials are carried into a reaction mixture in which they do not belong.

3. Persistence of a substance in soil, e.g., a pesticide, such that injury may occur subsequently to a new crop.

4. Persistence of a test substance in participants undergoing a cross-over clinical trial study, in which each participant randomly receives the placebo and test substance with an intervening washout period.