Can you help me define "tiers" please?

<p>Be careful of ‘tiering’ a school out of consideration…it can result in missing hidden gems. For example, University of Cincinnati is a [Tier</a> 3](<a href=“http://colleges.usnews.rankingsandreviews.com/college/items/3125]Tier”>http://colleges.usnews.rankingsandreviews.com/college/items/3125) according to USNWR but it’s [ranked</a> 1 & 2 in design and architecture](<a href=“Error | University of Cincinnati”>http://www.uc.edu/news/NR.asp?id=4872).</p>

<p>So, as is often advised, fit is more important than the USNWR rankings.</p>