A Test strategy would be at a higher level of abstraction
than a test plan.

Ideally a Test Strategy would be put down and test plan
would follwo drilling into the nitty grities of the Testing
to provide a complete picture.

A good analogy would be ,the difference would be the same as
between a product overview pamplet and a product usage
manual, the later being thoroughly detailed.

a.Test strategy is master testplan.It will talk about the 
Budget,Timelines,objective.
b.What is the technical architecture of the 
application/product ?
c.What are the various types of testing to be performed ?
d.What is the development methodology for the 
application/product ?
e.What should be tested and how ? What should not be tested 
and why ?
f.Should the entire product/application be tested as a 
whole or run tests only on a certain part of it? 
g.As new components are added to a large system, should the 
tests be re-run which have already conducted?
h.What are the tools that can be used? 
i.What should the resources be trained on?
j.When should the end-user be involved?
	
And testplan is written for each type of testing,Like 
system testplan,UAT plan,Performance testplan,
It is more specific to type of testing.
The test plan will answer the following questions:
What is being tested?  
1. What are pass/fail criteria? 
2. When will each test occur? 
3. What hardware and software environment is required? 
4. What features must be tested? 
5. What features will not be tested? 
6. What are the responsibilities of individuals and 
organizations involved in the project? 
7. Identify the various modules and decide which 
modules/functionalities will be tested. Clearly mention 
which items are out-of-scope for testing
8. List down the priority of testable items (conflict-
resolution between the various players is of importance)

test strategy: A high-level document defining the test 
levels to be performed and the testing
within those levels for an organisation or programme (one 
or more projects).

test plan: A document describing the scope, approach, 
resources and schedule of intended
test activities. It identifies amongst others test items, 
the features to be tested, the testing
tasks, who will do each task, degree of tester 
independence, the test environment, the test
design techniques and entry and exit criteria to be used, 
and the rationale for their choice,
and any risks requiring contingency planning. It is a 
record of the test planning process.