Dynamics versus Lexical scoping

[Jean-Paul Tea <jeanpaul@cs.washington.edu>]

I heard that lisp can either use dynamic or lexical scoping.  I don't 
know if this is the newsgroup to post the following question.  If it is 
not, I like to apologize.

My question is:
What is dynamic or lexical scoping?  What are the advantages and 
disadvantages of each?  

I try reading it in books, but they are so vague on the subject.

Thanks,

Jean-Paul