Maybe because we haven't lived through the admissions process yet, I have difficulty keeping certain facts in my head, such as the difference between early decision and early action. So here's a quick review. And you can also look at the College Board explanation here.
Think of admissions as non-restrictive and restrictive.
Non-restrictive plans have no strings attached. You can apply to as many colleges as you wish and don't have to commit until May 1.
These include Regular Decision (apply in January, learn about the decision between mid March and April); Rolling Admission (applications are reviewed as they arrive and then decisions are sent either as soon as possible or on specified dates); and Early Action (apply by an earlier deadline and receive a decision earlier than the usual date).
This approach makes sense for most students. It means more time to apply; allows colleges to see first-semester senior year grades; enables families to compare all acceptances and financial packages; and gives the student a few weeks to decide where to attend.
Restrictive plans include Early Decision (apply to just one college and agree to a binding commitment to attend if accepted; usually apply in November, learn outcome in December; if accepted, all other applications must be withdrawn) and Restrictive Early Actionn (apply early to only one college but the student is not committed to attend; usually apply in November, learn in December; don't have to make decsion till May 1 but not offered by many schools).
Early decision makes sense only if the student, without a doubt, knows that College A is the first choice. This can be one of the most competitive cycles for admission, but colleges also like to see students so interested that they are willing to commit. This is not a smart approach if you are seeking financial aid.
Hope this helps.
I also blog on college issues at nj.com, Parental Guidance.