<p>JoeCD, deferred by her ED means the school she applied to Early Decision (which at any college means that an acceptance requires the student to enrol) deferred her application to RD (did not make a decision, but instead put it in a stack to be re-considered for the people who applied for the Regular Decision deadline).</p>
<p>Decision day is the date (usually end of December and beginning of May) when colleges send out their decisions. Students can often get all of their decisions within a few days of each other.</p>