The principle of buoyancy, as described by Archimedes, states that an object submerged in a fluid experiences an upward force equal to the weight of the fluid displaced by the object. This principle explains why objects float or sink based on their density relative to the fluid. If an object's density is less than that of the fluid, it will float; if greater, it will sink. This concept has numerous applications in engineering, shipping, and understanding buoyant forces in various fluids.