This is the 11729th most frequent German word.
tui
The word "tui" is not a standard German word. It might refer to "TUI," a German travel and tourism company.
In this sentence, 'TUI' is used as a proper noun referring to a travel company.
Ich habe bei TUI eine Reise gebucht.
I booked a trip with TUI.
Here, 'TUI' represents the corporation where the sister held employment.
Früher arbeitete meine Schwester bei TUI.
My sister used to work at TUI.
In the given context, 'TUI' is used as a proper noun indicating an organization that provides cruise services.