The person or party who requests a service, places an order, or commissions work. Common in business and legal contexts.
We revised the design according to the client's request.
Used especially for the sender of a package, freight, or mail. Overlaps with 差出人 (さしだしにん) but 依頼主 emphasizes the requesting/ordering relationship.
Please fill in your address in the sender field of the package.
顧客 is a broader term for a customer or client in a business relationship, while 依頼主 specifically refers to the one making a request or placing an order.
Compound of 依頼 (irai, 'request') and 主 (nushi, 'master' or 'owner'). The reading ぬし for 主 is a native Japanese reading (kun'yomi) often used in compounds to indicate a person in a specific role.