What is code coverage?

(
  The number of lines being actually executed through all existing test cases
  ÷
  the total lines of code in a system component
) * 100 [%]

Test coverage is not equal to Code coverage.

There could be:

• Test coverage by feature
• Test coverage by instrumentation (test code coverage)
• Test coverage by GUI elements
• Test coverage by risks
• Test coverage by transition (of user between states)
• Test coverage by scenario (use cases)

A Test Coverage Matrix can be defined as a table used to assure that all the needed requirements, scenarios, or features are counted.