Lubricating oil, hydraulic oil, turbine oil, engine oil, butter, gear oil

What follows are all lubricants, with different viscosities and different uses

Lubricant is a general term. Hydraulic oil is also a general term; it differs significantly from lubricating oil in terms of its nature. Moreover, many fluids used in hydraulic systems are no longer oils in the strict sense, and it is more appropriate to refer to them as hydraulic fluids. Additionally, butter is a lubricant; it is not an oil, but rather a high-grade organic ester or soap. The several concepts listed by the original poster that definitely belong to lubricants include: turbine oil (steam turbine oil), engine oil (mechanical lubricant), and gear oil. Hydraulic fluids are divided into two main categories: water-based and oil-based. Car brake fluid belongs to the category of hydraulic oils. Butter generally refers to calcium-based greases, sodium-based greases, lithium-based greases, etc. Lubricating oil is in a flowing state under normal conditions, and it is generally used for lubricating machinery with high rotational speeds. Grease is in a paste-like state under normal conditions, and is generally used for lubricating low-speed or translational machinery.