Hydraulic fluid, crucial in hydraulic systems, transmits power, lubricates, and seals components. Various types of hydraulic fluids exist, including mineral oil-based, synthetic, and water-based fluids. Mineral oils, common due to cost-effectiveness, offer good lubrication. Synthetics, like phosphate esters, resist fire and extreme temperatures. Water-based fluids, environmentally friendly, suit specific applications, but require corrosion protection. Choose wisely based on system requirements.