Saturated and unsaturated elements?
Although I've never heard this terminology before, I'm pretty sure I can see what it means.

As you can see from this diagram, each increase in the principal quantum number (n), adds a new type of orbital to that shell.



The electron configurations of the group 15 elements are:

\begin{array}{|c|c|} \hline
Element &amp; Electron~configuration \\ \hline
\ce{N} &amp; 1s^2~2s^2~2p^3 \\ \hline
\ce{P} &amp; 1s^2~2s^2~2p^6~3s^2~3p^3 \\ \hline
\ce{As} &amp; 1s^2~2s^2~2p^6~3s^2~3p^6~3d^{10}~4s^2~4p^3 \\ \hline
\ce{Sb} &amp; 1s^2~2s^2~2p^6~3s^2~3p^6~3d^{10}~4s^2~4p^6~4d^{10}~5s^2~5p^3 \\ \hline
\ce{Bi} &amp; 1s^2~2s^2~2p^6~3s^2~3p^6~3d^{10}~4s^2~4p^6~4d^{10}~4f^{14}~5s^2~5p^6~5d^{10}~6s^2~6p^3 \\ \hline
\end{array}

$\ce{N, P}$ and $\ce{As}$ all have full penultimate shells, whereas $\ce{Sb}$ and $\ce{Bi}$ do not -  the $4 f$ and $5 f$ orbitals are unnocupied respectively. Therefore 'saturated' seems to refer to elements where the penultimate shell is fully occupied, and 'unsaturated' to elements where it is not.