Just to give a concrete example, here is Yale:
Applying to Other Colleges and Universities
If you are a Single-Choice Early Action applicant to Yale, you may apply to another institution’s early admission program as follows:
- You may apply to any college’s non-binding rolling admission program.
- You may apply to any public institution at any time, provided that admission is non-binding.
- You may apply to another college’s Early Decision II program, but only if the notification of admission occurs after January 1. If you are admitted through another college’s Early Decision II binding program, you must withdraw your application from Yale.
- You may apply to another college’s Early Action II program.
- You may apply to any institution outside of the United States at any time.
That’s a lot of exceptions!
I think the basic idea is they don’t want you applying normal EA I or ED I to any other private university in the United States. Other than that, you can find plenty of non-RD options, including EA II and ED II where available at US privates (with the understanding if you get a deferral and apply ED II and then get in, you are bound to go to the ED II school).