Meaning- "Sigma bonds can occur between any kind of atomic orbitals; the only requirement is that the atomic orbital overlap happens directly between the nuclei of atoms."?
Sigma (σ) bonds are formed by head-on overlapping of atomic orbitals.
This puts most of the electron density along the internuclear axis between the two nuclei.
Here are some examples of σ bonds,
Hydrogen has an
(From Google Sites)
Ethane has an
You can also have
(Adapted from Boundless)
In all of these σ bonds, the bonding electrons are on the internuclear axis between the two nuclei.