Test coverage is a black-box testing method that entails testing elements included in the functional requirements specification, software requirements specification, and other required documents. Since the tests are derived from these documents, there is minimal or no chance of automation.
For example, say you want to perform cross-browser testing on your web application to see if it renders properly in different browsers and operating systems. Your test coverage would equal the number of browser + OS combinations for which you have tested your web application's browser compatibility.