The Ental (usually shortened to en) is the currency that is found across all the Etrian Odyssey games. Used to buy everything, having more en is favorable than having less. Quests will sometimes give Ental as a reward, however missions will always give Ental. The Alchemist class has a skill called Alchemy, which turns resources that are discarded from the inventory into Ental.
While monsters and items can be similar across the series, the Entals given for selling items/drops will vary from game to game.