What is the difference between Test Plan and Test Strategy?

I would say that a strategy is a general rule or set of rules as to how you will achieve your objectives, such as the tools to use the outline processes to follow etc.

A plan is a more detailed specification of what the targets are and what needs to be done to reach those targets.

It's really a question of semantics, as long as everyone in the team has a clear idea of what to do, how to do it and when to do it, then success is guaranteed.

A test plan can be defined as a document describing the scope, approach, resources, and schedule of intended testing activities
The test levels to be performed in testing and the description of testing activities within those test levels is known as test strategy.