ARGENTAFFIN CELLS produce SEROTONIN (its precursor is 5-hydroxy -tryptamine).please explain what do this statement mean..........???????

Argentaffin cell are the flattened or round shaped cells occurring in the lining tissue of the digestive tract and containing granules thought to be of secretory function.The granules of these cells contain chemical called serotonin, which stimulates smooth muscle contractions that encourages the passage of food substances through the intestinal tract. 

Serotonin, also called 5-hydroxytryptamine,  is a chemical substance that is derived from the amino acid tryptophan. 

5-hydroxy -tryptamine is a precursor of serotonin means that serotonin is formed from the 5-hydroxy -tryptamine.