The Italian word biscotti originates from the Medieval Latin word biscoctus, meaning 'twice-cooked', which described items that were made from dough and baked twice, so they became very dry and could be stored for long periods of time. Such non-perishable food was particularly useful during journeys and wars, and twice-baked breads were a staple food of the Roman legions. Biscotti, in this sense, shares its origin with the English biscuit (from Old French biscuit), which is used for a wide variety of baked goods, biscuits, crackers, and breads, only a few of which are actually baked twice.

Source: Wikipedia