I finally have a better understanding of these "early admission plans".
For comparison purposes, regular application deadline is January 1, and results are normally released in end of March.
The "Early" part of these plans (Early Action, and Early Decision and Restrictive Early Action, Single Choice Early Action) refers to early application deadline, typically, November 1 of each year, and the early notification date, typically, in mid-December or January, or February.
To be considered for any Early admission plan, students must check a box in Common App and must submit all required documents before the Early deadline. Early Decision plan requires signature from the Student, the Parent and Counselor to agree that the decision is binding. Restrictive Early Action may also require signature.
Counselor can only send the student's transcript to one school only when the student is applying through Early Decision.
In return, students are notified of an admission decision well in advance of the regular notification date, typically, in mid-December or January, or February.
The difference is that Early Action acceptance is nonbinding. Students do not have to commit to attending the college. In fact, student can apply to other colleges during regular application cycle.
Early Decision acceptance is binding. Students are notified of an admission decision well in advance of the regular notification date AND students must make a DECISION NOW, student is expected to commit to attending the college.
In theory, students can apply to multiple schools via EA unless the EA plan is restrictive, then it prevents students from applying to other early plans.
Single Choice Early Action means that the student cannot apply to other Early Action colleges.