What do you call the part of a plant which is used for culturing?

An explant is the term for any piece of plant tissue (leaf, stem, root, meristem, etc.) that is excised from a donor plant and placed in culture medium for tissue culture. The explant serves as the starting material that will dedifferentiate, divide, and regenerate into a complete plantlet through callus formation or direct organogenesis. 'Scion' and 'stock' are terms used in grafting (the upper and lower parts respectively), while 'callus' is the undifferentiated mass of cells that forms from the explant during the culturing process, not the starting material itself.