1A suffix/noun meaning a person or office in charge of something (e.g., 'account clerk', 'guide'). In some official contexts it is written 掛 (kakari).
会計係は領収書を整理している。
The account clerk is organizing the receipts.
質問があれば総務係に聞いてください。
If you have questions, please ask the general affairs section in charge.
受付係が来場者の名前を確認した。
The receptionist checked the visitors' names.