What is the difference between Test Plan and Test Strategy?

A Test Strategy document is a high level document and normally developed by project manager. This document defines "Testing Approach” to achieve testing objectives. The Test Strategy is normally derived from the Business Requirement Specification document.

On the other hand, the Test Plan document  is derived from the Product Description, Software Requirement Specification SRS, or Use Case Documents.The Test Plan document is usually prepared by the Test Lead or Test Manager and the focus of the document is to describe what to test, how to test, when to test and who will do what test.