What is the definition of Business Development, and what is the job description of a Business Development Manager?

Dear Mahdi, this falls exactly in the meaning of Sales Development.

If Business Development was just what you stated, why wouldn't we then just call it "Sales development"?

Isn't the word "Business" wider than just the word "Sales", or in other terms, would you be able to restrict Business to the Sales side of it?

Business Development means sales. Someone who turns leads into opportunities and closes them. In some cases the term business development is used when the sale cycle is longer with mulitple points of entry.