If you woked on TFS on Microsoft platform, you migh see Test Plan on TFS. What is the Test Plan on TFS? We are creating test projects on development platform (visual studio). But I could not understand TFS Test Plan. Is this about code?
A Test Plan is part of Microsoft Test Manager, which is a tool for creating and running manual tests, and managing test/lab environments. Nothing to do with code, unless you're converting manual tests to automated tests (even then, the Test Plan isn't an important piece of that process).
A Test Plan is simply a container for Test Suites, which are in turn containers for Test Cases. Each level represents a finer degree of granularity, and each level has it's own associated metadata. This allows you to create sophisticated reports at various degrees of specificity.
Some examples of test plans:
There is a lot of metadata (builds, configurations, environments etc) that you can associate with a test plan, but when you get right down to it they are just containers for test suites, which are containers for test cases.