What is Electron-deficient and hypervalent molecules?

A molecule in which an atom has fewer than eight valence electrons is electron-deficient: in $\ce{BF3}$ boron has six. A molecule in which an atom of period 3 or beyond is surrounded by more than four pairs is hypervalent: in $\ce{PCl5}$ phosphorus forms five bonds, in $\ce{SF6}$ sulfur six. Molecules with an odd number of electrons, such as $\ce{NO}$ and $\ce{NO2}$, cannot satisfy the octet rule on every atom: one electron is unpaired.