EA is EarlyAction, which translates to early action. You can apply to several schools at the same time, and you can choose one after admission. Both are admission methods of opening the application earlier and closing the application earlier.
RD is a routine decision, which belongs to the case of normal application and is later than the above two public applications.
RO is rolling, which translates to rolling admission. That is, the school does not have a clear application deadline. As long as the school has a position, it can consider enrolling students.