Hardtack (or hard tack) is a simple type of biscuit or cracker, made from flour, water, and sometimes salt. Inexpensive and long-lasting, it was and is used for sustenance in the absence of perishable foods, commonly during long sea voyages, land migrations, and military campaigns. The name derives from the British sailor slang for food, "tack". It is known by other names such as brewis (possibly a cognate with "brose"), cabin bread, pilot bread, sea biscuit, sea bread (as rations for sailors), ship's biscuit, or ship biscuit, or pejoratively as "dog biscuits", "molar breakers", "sheet iron", "tooth dullers", or "worm castles". Australian and New Zealand military personnel knew them with some sarcasm as ANZAC wafers (not to be confused with Anzac biscuit).