What does it mean to be an ivy walk on?

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<p><a href=“http://talk.collegeconfidential.com/athletic-recruits/910372-what-does-recruited-walk-ivies-even-mean.html?highlight=walk[/url]”>http://talk.collegeconfidential.com/athletic-recruits/910372-what-does-recruited-walk-ivies-even-mean.html?highlight=walk&lt;/a&gt;&lt;/p&gt;