small amount of an easily detected substance that can be used to follow and quantify the flow of materials or movement of organisms not otherwise visible or detectable by ordinary means, a substance (as a radioactive isotope or a dye) with distinctive properties that is introduced into a system so that its subsequent distribution may be readily followed

mingit sündmust v olekut näitav vahend v andmeelement; MARC-vormingus muutpikkusega välja algul paiknev andmeelement, mis interpreteerib v täiendab välja andmeid