what does a circle with line through it mean
No symbol The international prohibition sign (official name), (also known as a no symbol, no sign, circle-backslash symbol, nay, interdictory circle, or universal no) is a red circle with a red diagonal line through it (running from top left to bottom right), completely enclosing a pictogram to indicate something is not permitted. The prohibition sign is sometimes seen in all-black, where color is not available.
Curvature One way is geometrical. It is natural to define the curvature of a straight line to be constantly zero. The curvature of a circle of radius R should be large if R is small and small if R is large. Thus the curvature of a circle is defined to be the reciprocal of the radius:[2]