A cuboid.
There is no 3D shape with 6 faces: 4 rectangles and 2 triangles. See the link for all forms of hexahedra.
A 3-d shape with 6 equal faces is a cube. It has 6 squares as it's faces. A 3-d shape with 6 equal faces and only 2 squares is a rectangular prism. It has 2 squares and 4 other rectangles (squares are rectangles too) as it's faces.
The question is somewhat confused. It has "... 6 flat SQUARE faces 2 are SQUARE and 4 are RECTANGLES ...." Assuming the first part is wrong, the shape is a cuboid.
No 3D shape with FLAT SIDES has exactly 3 faces. 4 is the minimum.
That 3D shape is called triangular pyramid.
it is a strong inadiquate word that describes a 3d shape. A tetrahedron.
2 squares & 4 rectangles.
A tetrahedron.
A triangular pyramid.
triangular pyramid
A square based prism.