An adverb meaning one by one; one at a time; in turn, doing something sequentially rather than all at once.
面接は一人ずつ順番に行いますので、少々お待ちください。
Interviews will be conducted one person at a time, so please wait a moment.
お菓子を一人ずつ配ってください。
Please hand out the snacks one by one to each person.
店員が一人ずつ丁寧に対応してくれた。
The clerk attended to each person carefully, one at a time.