Test plan is a document that describes the
scope,purpose,objective & risks

Test Strategry:the way that we are approaching for testing

Test Strategy: This is high level document which defines 
the approach for testing the overall product

Test Planning: Test plan defines the specific information 
about how to drive, track and record the test efforts along 
entrance exit criteria, resource planning, risk and 
contingency plans, etc. Test planning also define the 
milestone and schedules to effectively manage the efforts 
and performance.

Test Plan:describes how testing is to be carried out in an 
efficient, effective an dan optimised way by giving info. 
abt coverage of testing, test deliverables, test 
environment, resource planning, scheduling, risks and 
contingensies, Assumptions and Approval info.
Test stategy:involves in identifying the areas of s/w that 
needs to be during the system test plan.This test strategy 
document is prepared by the test lead which will define the 
exact testing approach that is to be followed by the 
testing team in s/w testing by giving the info abt levels 
and types of testing,test design techniques,test 
metrics,automation plan and list of automation tools.

Test Strategy is a High level document in detail it explains
about the work flow of testing along with all the requirements .

Test plan is a document comes under the test strategy.