So many people ask if they should apply by the priority deadline that I felt it was worth sharing my understanding of why it is in your best interest to submit your application by November 1st. (For newbies, I am a parent of a recent grad (mechanical engineering) and an alum, but have no “insider” info, so this is just based on my own experience and info I got when I went to info/admission sessions over the course of several years.)
Understand that unlike other schools, Maryland’s priority application is NEITHER an early decision NOR an early action.
The first term, early decision, involves a binding commitment to the school whereby you cannot apply early to any other school and should they admit you (and you will know by December), you are committed to enrolling there.
The second term, early action, is not binding for enrollment, but in many cases does restrict you from applying early to other schools, and also notifies you of their decision in December.
So, WHAT is priority application then? It is an earlier deadline to submit your application that is entirely non-binding. You must apply by November 1st (meaning everything must be in by November 1st to be considered complete) and you will be notified of their decision by February 1st (typically the last week of January, but NOT sooner than that despite a plethora of unsubstantiated rumors).
WHY apply priority?
- It gives you the best shot at admission since the majority (anywhere from 80-90% - a lot of people say closer to 90%) of the incoming freshman class is accepted from among the priority applications.
- It is the ONLY WAY TO BE CONSIDERED for any MERIT SCHOLARSHIPS and special living-learning programs such as HONORS COLLEGE, COLLEGE PARK SCHOLARS, CIVICUS, ETC.
- That bears repeating.... It is the ONLY way to be considered for any MERIT SCHOLARSHIPS (which is different than financial aid), so if you wait to apply, you will have a zero chance of merit money, NO EXCEPTIONS.
- There only possible exceptions for being accepted living-learning programs for those that do not apply by Nov 1st (that I am aware of) are the engineering living-learning programs (FLEXUS for girls http://www.wie.umd.edu/undergrad/flexus and VIRTUS for guys http://www.seeds.umd.edu/programs/virtus) since you actually have to apply to that (not automatic consideration) and that is done in May, so I don't believe university application timing is relevant but only goes by direct admission to engineering for eligibility and submission of Flexus/Virtus program application on time.
Let me explain #1 further and what that means for you. Yes, if you apply by Nov 1, you will be applying with the largest pool of applicants, and your grades from senior year won’t be in to show a continued improvement, and your currently available standardized test scores may not be as high as the test you plan to take in November (so after the application deadline). HOWEVER, you will also increase your chance of being one of the admitted students since they will make the most offers of admission to November 1st applicants.
As a simplified example to understand what I mean, let’s say there are 1,000 offers of admission that will be made. At the very least, 800 of those offers (potentially and likely more) will be used for Nov 1st applicants. So, if you apply by Nov 1st, you have a shot at one of 800 spots. However, if you wait until January 1st because you think you will be a stronger applicant by then (improved grades, test scores, whatever) you have a shot at only one of 200 spots. The competition for those 200 spots is going to be tougher.
Not only is it tougher to get a spot if you wait until January deadline, but you will have sacrificed your eligibility for any merit money (however, financial aid for need will not be affected as long as you submit your FAFSA in time). Even if you are doubtful about a merit scholarship, you still are ALSO sacrificing your eligibility for any special living-learning programs.
So, my best advice to ALL applicants is to get everything submitted in the next few weeks (follow up with that teacher, guidance counselor, college board, etc) to make sure recommendations, test scores and transcripts are sent in time to be received by Nov 1st.
Submit your application at the very least a few days before Nov 1st because you never know what unexpected things may happen on the internet, or your computer, or your power (yes, outages do happen unexpectedly), so better safe than sorry.
NOTE: With the huge influx of data, the application system takes a while to update individual accounts to note items received. So, if your Maryland application portal is not showing that something is “received” but you have verified with the sender that it was indeed sent out in time, you should be fine.
Best of luck to all applicants. 
Maryland is an awesome school… GO TERPS!