While there are few defintions now, there will be more in the near future. Thank you for your patience.
Query letters are instrumental in providing information to an editor in a concise way.
If you know how to write a good query letter, your chances of selling your work will be much better. It is the name of the author appearing with the work when it is published. A Brief letter, usually accompanying a manuscript that an editor has requested to see. The Cover Letter is NOT a query letter. A collection of works by either one author, or several.