Seed, seedling, sprout, green herb, fibrous root – what's what?
Seed = the embryo within the seed
The seed is the blueprint of the plant that is contained within the seed. The germ or plant embryo is well hidden within the seed. It contains as precursers the preliminary seed leaves, the preliminary roots and the preliminary stem. None of these plant parts are yet differentiated.
Sprout = young leaves and stems
In the proper meaning of the word, the sprouts describe only the above ground parts of the seedling, namely the stem and the leaves. Technically speaking, the roots are not part of the sprouts. For the sprouting process, however, one normally uses the term 'sprout' to describe the entire seedling. In most cases, the harvested sprouts are still so immature that they still lack functioning roots.
Green herb = green juvenile plants
When the developing plant has reached the 'green herb' stage, the stems grow orderly upwards and green leaves will have formed in the upper part of the plant. The roots are either tapping into a substrate or they are intertangled and are no longer edible. The most popular green herb plant is cress. Store-bought cress is the fully developed green herb.