In the context of the Euler-Lagrange equations, stationarity refers to the condition where the action integral, defined as s = ∫ L dt, is at a stationary point along the path of a particle. This does not imply that the integral is constant, but rather that its variation is zero, indicating that the action is minimized or maximized for the actual path taken. A stationary point occurs when the derivative of the action with respect to the path is zero. The Euler-Lagrange equations are derived by applying this principle of stationarity to the action. Understanding this concept is crucial for analyzing the dynamics of systems in Lagrangian mechanics.