Specialized lubricating oil supplied between cutting tools and workpieces during cutting, grinding, and drilling operations in metalworking. Used in machining operations on machine tools such as lathes, milling machines, drilling machines, and grinding machines to extend tool life, improve machining accuracy, and enhance surface finish. Classified into water-soluble cutting oils (emulsion type and solution type) and water-insoluble cutting oils (straight oils), with optimal viscosity and additive formulations selected according to workpiece materials (steel, aluminum, stainless steel, etc.) and machining methods. Unlike general lubricating oils and greases, these feature specialized formulations focused on cutting performance and cooling capabilities.