Credits are the currency in the world of Xenoblade Chronicles X. The party can obtain credits from completing missions, selling items in Armory Alley, or from Treasure Boxes found on Mira.
The sell price listed in item infoboxes is the amount received when selling that item. For weapons and armor, the purchase price, the amount of credits needed to buy the equipment from Armory Alley, is 100 times the sell price.