For the most part a trademark is only good within the same industry.
Universal cannot make an animated film called Moana about a princess, because Disney has already.
Disney cannot make a soap named "Moana" because Bath and Bodyworks owns the TM on that already.
MOANA Trademark - Registration Number 3455531 - Serial Number 78846954 :: Justia Trademarks
No one but "Seresin Estate Limited" can make wine named Moana because they registered for that industry first.
MOANA Trademark of Seresin Estate Limited - Registration Number 4055103 - Serial Number 85147599 :: Justia Trademarks
Etc. etc, for 79 different categories of services for the word Moana.
And to get really specific, Disney only owns the trademark for the term "DISNEY MOANA," and not Moana on its own.
DISNEY MOANA Trademark Application of Disney Enterprises, Inc. - Serial Number 86453776 :: Justia Trademarks
They have trademarked "DISNEY MOANA" in more than 50 service and product categories (none of which are water slides.)
EDIT: Sorry for the info dump. I've been involved in legal situations regarding infringements on my own marks in the past. As long as Universal doesn't cause any brand confusion between their slide and the Disney film they'll be fine. Like if they have a cartoon princess character on the sign for the slide they may get in some trouble. But barring that they'll be just fine. The word means water in this case.