A letter of inquiry, also known as a prospecting letter or letter of interest, is sent to companies that may be hiring, but, haven't listed specific job openings.
example :
http://bagaskawarasan.files.wordpress.com/2012/11/inquiry1.jpg
Order letter Definition:
An order letter is a business letter which confirms the details of a purchase of services or goods from one party to another. Also, such terms as a letter of order or a PO (purchase order) can be used. The purpose of an order letter is to give the necessary instructions to the seller to fulfill an order successfully. The paper track of a particular transaction starts with it.
example :
http://static2.businessinsider.com/image/500d57fd6bb3f7705f000002/jack-daniels-cease-and-desist-order.jpg
quote :
http://jobsearch.about.com/od/jobsearchglossary/g/inquiryletter.htm
http://bestletterhelp.com/business-letters/how-to-write-order-letter.html
