Iggy's right, tier 1 is the top 50 tier 2 is 51-100 tier 3 and four aren't given any rank but just alphabetical order. The top schools are known as the top 10 (Usually Yale, Harvard, Stanford, Columbia, U of Michigain, Berkley (Boalyon Hall), Boston, UCLA, Cornell, and Georgetown grace these spots).
But according to many scholars, Ranking Law Schools in general is exceedingle subjective and should only serve as a general starting point in comparing law schools.