Terminology:
  [Ref: Cascading Style Sheets: The Definitive Guide, 2nd Edition, sect 2.1.1]

 p { color: red; font-family: sans-serif; }
     
 Term             Which part is described
========          =======================
 rule               p { color: red; font-family: sans-serif; }
 selector           p 
 declaration            color: red;
 property               color       
 value                         red 
 declaration                        font-family: sans-serif;
 property                           font-family
 value                                           sans-serif
 declaration block    { color: red; font-family: sans-serif; }