Acnode

An acnode is an isolated point not on a curve, but whose coordinates satisfy the equation of the curve. The term "isolated point" or "hermit point" is an equivalent term. Acnodes commonly occur when studying algebraic curves over fields which are not algebraically closed, defined as the zero set of a polynomial of two variables. For example the equation has an acnode at the origin of , because it is equivalent to and is positive for , except when . Thus, over the real numbers the equation has no solutions for except for (0, 0). In contrast, over the complex numbers the origin is not isolated since square roots of negative real numbers exist.
See more at Wikipedia.org...

(n.)
An isolated point not upon a curve, but whose coordinates satisfy the equation of the curve so that it is considered as belonging to the curve.
  

acnode
(hình học) điểm cô lập (của đường cong)
(C) 2007 www.TừĐiểnTiếngViệt.net

NODO ISOLATO [MATEMATICA]. PUNTO DOPPIO ISOLATO [MATEMATICA]