Essentially how it works is you start submitting your applications in November through January, and then universities look at all the applicants and choose a number of people they want to accept and send out the first round of acceptances, and they keep doing that over and over again until the program is filled up.
Let's say the university wants 100 people in their program, so it sends out acceptances to their top 100 picks among student applications. 70 say yes and 30 say no (whether that be because they changed their mind, or they want to go to a different university that accepted them, or something like that). Then the university would go through the applicants again and send out acceptances to their next 30 picks. And this goes on until every spot is filled. If you don't get accepted (i.e. get rejected), you don't actually find out until June, which is when the current school year ends.