This is the 768th most frequent Japanese word.
トイレ
Toilet.
トイレ is being used to refer to the location of a restroom.
トイレはどこですか？
Where is the restroom?
トイレ refers to the act of visiting a restroom in this contextual usage.
トイレに行ってもいいですか？
May I go to the restroom?
トイレ is used to describe a specific restroom and its condition.