I wonder if there is a name for a irregular convex octahedron, with 6 vertices, that consist of two sets of 4 identical isosceles triangles. It could be created by intersecting two rhombic prisms, or by stretching the square base of a regular octahedron into a rectangle.
Forms like these can be seen on natural orthorhombic crystals like topaz. See the images.
I would call it a rectangular bipyramid (the comment pointing out that it is an octahedron is correct; anything with 8 faces can be referred to as an octahedron, including things like Dürer's solid. But, I generally associate "octahedron" with the regular octahedron).
A [blank] bipyramid is the shape obtained by gluing the bases of two [blank] pyramids together. So a regular octahedron is a square bipyramid; the classic Sims plumbob is a (regular) hexagonal bipyramid, and so on.