"The atomic orbitals also have characteristic shapes. For example a s orbital is spherically symmetrical, and a p orbital has two areas with a nodal plane between them. Molecular orbitals are like atomic orbitals, but spread throughout the entire molecule. Molecular orbitals are formed through a process of combining atomic orbitals. A molecular orbital with cylindrical symmetry around the internuclear axis is called a sigma orbital (because it looks like a s orbital when viewed along the axis and it has zero angular momentum around the internuclear axis)."