What are the differences between Test Plan and Test Strategy ?

To find out the difference between Test Strategy and Test Plan, check below points:

Point of Distinction Test Plan Test Strategy
About It is designed with an objective to include all details related to the testing like what to test, how to test, when to test, and who will be testers etc? Test Strategy is a high-level document that defines the proper approach for software testing. 
Derived From SRS - Software Requirement Specification BRD - Business Requirement Document
Developed By Test Lead / Test Manager or Project Manager Business Analyst or Project Manager
Update Frequency A Test Plan is updated frequently as soon as new features or changes are introduced. Not Updated Frequently
Project Relation Always specific to a particular project Normally for a complete organization. Although it can be specified for a particular project.
What it describe It describes the whole testing activities in detail - the techniques used, schedule, resources etc. It describes the high-level test design techniques to be used, environment specifications etc.
Components Components of Test plan include - Test plan id, features to be tested or not to be tested, test techniques, testing tasks, features pass or fail criteria, test deliverables, responsibilities, and schedule, Test Environment, Entry Criteria, Exit Criteria etc. Components of Test strategy includes - objectives and scope, documentation formats, test processes, team reporting structure, client communication strategy, Business Issues, Testing Approach, Test Deliverables, Defect Tracking Approach, Training, Automation, Risks etc.
 
Existence Exist Individually In small organisation Test Strategy is part of Test Plan 
Identify Possible Risks or Issues. A test strategy helps to abstract information that does not project specific but it can be used with the test approach.