压缩饼干是饼干的一种，一般由膨化粉、白糖、花生油、食盐、芝麻、水制作，多用于紧急情况下的救急之用。

压缩饼干一般为长方形的一片，非常坚硬，不易变软。由于体积较小，适宜长期保存和运送。压缩饼干热量很高，能有效补充体力和矿物质，满足一个静止不动的成年人几天的需要。现代压缩饼干多为真空包装。

地震、洪灾、台风等情况下，缺少食物，这时压缩饼干就能起到救急之用。食用压缩饼干能延长幸存人员等待救援的时间。压缩饼干可以干吃，也可以边喝水边吃。

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).