Test strategy is all about how to test a piece of code and 
test plan is about when to test and in what sequence

Test Strategy:
It defines what levels of testing will be conducted and  by 
whom,the TestPlan and how the testing will be 
executed,measured,managed and controlled.
To improve the efficiency and effectiveness of the testing 
process there are different levels of testing perormed at 
diff stages proir to the implementation of solution.
Is a document that doesnot change from project to project.
Test strategy clarify the major tasks and challenges of the 
test project is to establish the framework for testing the 
system.
Gererally initiated by ProjectManager,where he figures out 
what tests to be applied on build and he decides what are 
the relevant tests to be done on the receieved build.


TestPlan:is a comprehensive doc which describes the scope 
of testing,exit and entry criterias,environment,features to 
be and not to be tested ,testing startegies,risks and 
contingencies,staffing and training 
needs,responsibilities,suspension criteria and resumption 
requirements,Test deliverables..and includes many more 
details.
Usually each company will have test plan template which is 
usually followed.

Test Plan: Test plan is a Document, developed by the Test 
Lead, which contains "What to Test","How to Test", "When to 
Test", "Who to Test".

Test Strategy is the plan for how you are going to approach 
testing for the developed application.