👉 A fluid, in the context of medical terminology, refers to any substance that circulates through the body's vascular system, typically in liquid form. This includes blood, which is the most common fluid, composed of plasma, red blood cells, white blood cells, and platelets. Other fluids include synovial fluid, which lubricates joints, cerebrospinal fluid that cushions the brain and spinal cord, and mucus, which helps protect and moisturize surfaces in the respiratory and digestive tracts. The assessment of fluids often involves evaluating their composition, volume, and function to diagnose and manage various health conditions.