Rolling admission is the admission process in which the application period ranges from 6 to 8 months. Colleges in the US provide flexible application window to students to send in application forms. As the name suggests, colleges with rolling admission review applications as they arrive on a rolling basis which means instead of collecting everyone's applications, reviewing them all, and sending out notifications to all applicants together, admission committee consider applications as they arrive. The application process does not have strict deadlines, students get a time frame of around 6 months starting from August till February in which they can send in their application forms. Since the forms are reviewed as they are received, university notifies the applicant of their decision within a few weeks from submission.
While no Ivy League schools receive applications on a rolling basis, there are several reputable institutions like Indiana University, Penn State, Rutgers, etc. that participate in this admission method.
Less stressful for students and the university. Students can take time to carefully review their application and the stress of deadline is eliminated. The institute receives applications continuously rather than in bulk and is thus able to spend more time on each application individually.
Less competition. Applying early has advantages, as the applications are reviewed when they arrive they are not judged in direct competition with everyone else who has applied.
More time to plan. By setting a deadline for yourself, you can plan out when to take the SAT or ACT, when to ask for recommendation letters, and when to start writing your college essay.
Flexiblility. Rolling admission decisions aren’t binding. You'll have up until the national response date of May 1 to decide where to enroll.
Even if there is no deadline, it is advised to send the application early since the admission is provided on a first-come-first-serve basis. Most rolling admissions school have limited number of student slots which get filled rapidly. If you apply late, then there is a possibility all seats may be filled.