equilateral, isosceles, and scalene.
You would cut off a corner.
No, a cube cannot have an octagonal cross-section.
Cross section of a Cube90 Degree Vertical & Horizontal cross sections of a Cube are square. Brahmajyothi
It is a triangle.
A cube and an equilateral triangle based pyramid
Here are three: equilateral triangle, square, and cube
It depends on the angle of the plane of the cross section. If it is parallel to the cube's face (or equivalently, two adjacent edges) the cross section will be a square congruent to the face. If the plane is parallel to just one edge (and so angled to a face), the cross section will be a rectangle which will have a constant width. Its length will increase, remain at a maximum level and then decrease. If neither, it will be a hexagon-triangle-hexagon-triangle-hexagon (triangles when passing through a vertex).
A square, a cube, a diamond, a equilateral triangle, a triangular based pyramid made of equilateral triangles...
It is a square.