Carbohydrates: What does "typical nature" mean here?
Looks like your book's come up with a "localized" version of the D-L notation.

$\ce{D-L}$ notation in brief: A $\ce{D}$-sugar has the $\ce{-OH}$ group (on the stereogenic carbon atom on the parent chain, furthest away from the aldehyde group) facing right in the Fischer representation.
Likewise an $\ce{L}$-sugar has the $\ce{-OH}$ group facing left.



What your book's attempting to do is extend the $\ce{D-L}$ classification to individual carbon atoms in the parent chain.



The "3rd($\ce{L}$)" bit is supposed to mean, "3rd carbon atom has an $\ce{L}$-type configuration".

The "2,3($\ce{L}$)" bit is supposed to mean, "2nd and 3rd carbon atoms have an $\ce{L}$-type configuration".

You can figure out the rest ;-)



This appears to be some sort of memory aid to help you remember the configuration of the various kinds of 6-carbon sugars. The "typical nature" term was, in all likelihood, concocted by the authors (perhaps they thought it sounds better than "mnemonic"?)