In a good interview, this question changes the room. "What would success look like after 90 days?" forces the hiring manager to stop sounding vague.
If they answer with a calendar, a project, and a name, the job has shape. If they answer with buzzwords, you're being sold a blank notebook.
The best replies sound concrete: ship this report, meet these 3 people, fix this broken process.
A real role has a first chapter.