Early Access Program (EAP) is a way to to deliver specific features early to a group of people who will test and provide feedback on that feature.
InterSystems has been releasing different versions (or pieces) of software over the last few years and improving features before they were released. Some examples so far: Columnar Storage; Built-in Python; FHIRSQL; and others.
But one characteristic of EAPs is that they may not be available to everyone. You have to enroll in the Program.