Hydraulic fluid is a specialized liquid used in hydraulic systems to transmit power. It operates by transferring force through a confined fluid, allowing machinery to perform tasks like lifting, pressing, or moving. Common types of hydraulic fluids include mineral oils, water-based fluids, and biodegradable options. The properties of hydraulic fluid, such as viscosity and temperature stability, are crucial for efficient system performance. Additionally, hydraulic fluids often contain additives to prevent corrosion, reduce foaming, and improve lubrication. Proper maintenance and selection of hydraulic fluid are essential for the longevity of equipment like excavators and forklifts.