Eulerian coherent structure

In applied mathematics, objective Eulerian coherent structures (OECSs) are the instantaneously most influential surfaces or curves that exert a major influence on nearby trajectories in a dynamical system over short time-scales, and are the short-time limit of Lagrangian coherent structures (LCSs). Such influence can be of different types, but OECSs invariably create a short-term coherent trajectory pattern for which they serve as a theoretical centerpiece.

Source: Wikipedia — Eulerian coherent structure (CC BY-SA 4.0)