A Fixed Point for which the Stability Matrix has one zero Eigenvector with Positive Eigenvalue .
See also Elliptic Fixed Point (Differential Equations), Fixed Point, Hyperbolic Fixed Point (Differential Equations), Stable Improper Node, Stable Node, Stable Spiral Point, Stable Star, Unstable Improper Node, Unstable Node, Unstable Spiral Point
Tabor, M. ``Classification of Fixed Points.'' §1.4.b in
Chaos and Integrability in Nonlinear Dynamics: An Introduction. New York: Wiley, pp. 22-25,