-- an emerging trend in admissions that allows students to apply early for admission to the college of their choice and receive a decision well in advance of the normal response dates in the spring. Unlike Early Decision, you are not committed to enroll at that particular institution, and you can compare offers from other schools before making a final decision on what college to attend. Note: Applications are due much earlier for early decision requests and require more planning.

Early Decision
-- a binding agreement between the applicant and the college that basically states that, if accepted, the student agrees to attend the college. While you are still permitted to submit regular decision applications to other colleges, once you have been accepted through early decision, you are asked to withdraw all your other college applications. Therefore, it is wise to only apply to one school under an early decision option. Early decision is a great idea for students certain of their college choice. Note: Applications are due much earlier for early decision requests and require more planning.

Open Admissions
-- an admissions procedure used by some colleges, often community colleges, in which students are admitted regardless of academic qualifications.

Regular Admissions
-- the typical admissions process for college-bound students who do not have a clear favorite choice. With this method you send in your completed application about midway through your senior year of high school (typically in January or February, but earlier is always better, and you should check each college for deadlines), and each college notifies you of their decision later in the Spring (often early April). When you apply through the regular admission channels you have no obligation to attend any of the schools to which you have applied. Compare to Early Action and Early Decision.

Rolling Admissions
-- an admissions policy in which the college you apply to accepts applications throughout the year, reviewing applications as they arrive, and sending decision letters as soon as they are made. More traditional admissions policies have an application deadline in early winter (typically January or February), after which all applications are reviewed, and students are notified of decisions in late spring (between March and April).

Source:
http://www.quintcareers.com/college_planning_tutorial/college_admission_choices.html