Octahedron
An octahedron is a space figure that has eight sides.A regular octahedron has an equilateral triangle for each of its eight sides. Or if you prefer, it has two pyramids hooked together at the base.

Formulae used
\[volume = \frac{\sqrt{2}}{3}a^{3} \]
\[Surface\: area = 2\sqrt{3}a^{2} \]