The overview section of a test plan allows me to introduce readers of the plan to my test project, including what's to be tested and the general test approach. What I've found is that oftentimes managers one or two levels above me don't really have a good idea of what testing buys them. In the overview, I present a concise explanation of my goals, methodologies, and objectives. Although this section should be fairly brief, it's often useful to include simple pictures or charts. You might want to illustrate concepts such as the architecture of the system under test, the decomposition or segmentation of the system for component or integration testing, or how this test effort fits into other test efforts that might precede, run concurrently, or follow.