In "Fullmetal Alchemist" (鋼の錬金術師, Hagane no Renkinjutsushi), the concept of "equivalent exchange" is indeed central to the story. The specific phrase used in the series is "等価交換" (とうかこうかん, tōka kōkan), which translates directly to "equivalent exchange" in English. This principle governs alchemy in the series, stating that in order to obtain something, something of equal value must be given up.