The term principal case refers to a legal case that is deemed basic to understanding a legal principle. As a result, it may also refer to the case in a casebook that introduces a discussion of that principle. ... Found on http://en.wikipedia.org/wiki/Principal_case
1) Legal terminology 
The term principal case refers to a legal case that is deemed basic to understanding a legal principle. As a result, it may also refer to the case in a casebook that introduces a discussion of that principle. ...