question from do carmo diff. geometry I am studying differential geometry myself from Do carmo and i didn't understand the question :

show that if a surface is tangent to a plane along a curve , then the points of this curve are either parabolic or planar .

At the question i didn't understand the sentence ' surface is tangent to a plane along a curve ' 
Please firstly help  me about it and later maybe hints for solution   

Let $\pi$ be your plane, and $C$ some curve contained in $\pi$. The meaning of your problem would be that the surface $S$ is tangent to $\pi$ at all points $x\in C$. In other words, the surface touches the plane along the curve $C$ (in a tangential way).
For instance, the plane could be the $xy$-plane, and your surface could be a torus that rests on this plane. Then the point of contact between the surface and the plane is a circle.
