On their website, it says "If you accept our offer, you must withdraw any applications you have pending at other colleges or universities."I was wondering if that applied to my waitlists at other schools? Or just the schools I have already been admitted to?
If you applied ED (early decision) to NYU, then yes, you must withdraw all other applications.
If you did not apply ED to NYU, then more information is needed.
Issue: Does NYU consider a waitlist decision as a “pending application” ?
Contact NYU admissions & ask.
It’s not usually expected that you withdraw from waitlists afaik. However if you accept a position off a waitlist you will need to immediately withdraw from NYU and will lose your deposit.
If you had to withdraw from your waitlist with a deposit, waitlists would cease to exist.
All students on waitlists have accepted admission at another institution.
I would check the NYU literature if you are concerned and to be completely safe from an ethics perspective.