written request; application form
A formal document used to request or apply for something, such as a service, estimate, or permission. Common in business and official contexts.
I sent a written request to the business partner to get an estimate.
Those wishing to participate, please fill out the prescribed application form.
依頼 is the general act of requesting or entrusting, whereas 依頼書 is the physical or digital document that formalizes that request.
Compound of 依頼 (request, entrust) and 書 (document, writing). The word follows a common pattern for naming formal documents in Japanese.