The test strategy describes how - the overall test process, the techniques and practices used, design of test cases, selection of cases for retesting or regression, management and maintenance of the test environment, and the tools to support all of these. In some cases, the test strategy may also describe who - the structure of the test organization, who is responsible for creating or maintaining tests or test environments, and so on.
The test plan identifies what - the features that are being tested, the test cases that are being executed, the risks that have been identified. Often, it also identifies a schedule for testing and may also include specific responsibilities for executing against the test plan.
I don't think that it's necessarily true that a test strategy is static while a test plan is dynamic. A test strategy is probably updated much less frequently than a test plan and likely exists at an organizational or product level. The test plan likely exists at a release or iteration level. You may have multiple test plans for different executions of testing.