Descriptions are the basic syntax in Noos.
Just as Prolog in based in first order (Herbrand) terms, and Lisp or
Haskell are based in 
-terms, Noos is based in feature terms
(cf. feature terms in Chapter 3).
Descriptions are the syntax Noos uses
for constructing feature terms and is based on lists (like Lisp) that start
with the define
token.
There are two main kinds of descriptions: concept descriptions, that build constant feature terms--explained in the next section--and method descriptions, that build evaluable feature terms), explained in § 2.3.