A function 
has a spinode (also called a horizontal cusp) at a point 
if 
is continuous at 
and
 |
from one side while
 |
from the other side, so the curve is continuous but the derivative is not.s
Spinode
See also
Acnode, Crunode, Cusp, TacnodeExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Spinode." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Spinode.html