What is a plane figure obtained by slicing a solid with a plane?

Answer 1

That depends on the solid that you are slicing.

If the solid is a cylinder, you can make a circle by slicing horizontally,

or an ellipse by slicing diagonally.

If the solid has a square "base", then you can make make squares,

rectangles, and even hexagons.

If the solid is a cone or better yet a double cone, you can construct

the conic sections (circle, ellipse, parabola, hyperbola).

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Answer #2:

The tidiest answer to the question is: A "section" is.