What does a radical mean here?
A radical, according to the IUPAC, has an unpaired electron. Radicals may or may not be ions. 


  A molecular entity such as $\ce{.CH3}$, $\ce{.SnH3}$, $\ce{Cl.}$ possessing an unpaired electron.


http://goldbook.iupac.org/R05066.html

Contrary to your book's claim, the sodium ion is not considered a radical. It actually has all its electrons paired. It is isoelectronic with helium. 

Regarding your book's usage of "radical:" your book's terminology is outdated. Here is the IUPAC statement on your book's usage of the term:


  In the past, the term 'radical' was used to designate a substituent
  group bound to a molecular entity, as opposed to 'free radical', which
  nowadays is simply called radical. The bound entities may be called
  groups or substituents, but should no longer be called radicals.