切削液，是一种特别为机械加工而设的冷却剂和润滑剂。其中包括油、油水乳化液、膏剂、凝胶、气雾、空气或其他气体。他们可能会从石油馏出物、动物脂肪、植物油、水和空气、或其他原材料。视情况而定，所用不同类型的切削液，它可能被称为切削油、切削液、冷却液、或润滑剂。

取决于工件材料，大多数金属加工过程可从切削液的使用中受益，但亦有例外情况，例如是加工铸铁和黄铜，由于切屑多呈短屑状，混合切削液后反而容易堵塞退屑信道，令切削性能下降。

良好的切削液的应具备的性能：

Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases. They may be made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant.