Strictly speaking, they are not the same thing, although people often use them interchangeably. "Hydraulic fluid" is a broad umbrella term covering all liquids used...

The correct transmission fluid for your vehicle is typically specified in your owner's manual, stamped on the transmission dipstick, or identifiable using your Vehicle Identification...

Well, um, not at all. Differential fluid is a subcategory of gear oil—think of it as a "high-viscosity, heavy-duty lubricant." It is fundamentally different from...