What the percentage counts
Line coverage counts the lines of code that automated tests run. If it is 80%, the tests ran 80% of the lines counted in the report. Branch coverage checks whether tests followed both sides of a decision, such as a payment that succeeds or fails.
Running code is not checking it
A test can run a line without checking whether it gave the right result. Even 100% coverage cannot prove that software works.
Teams use coverage to find gaps, especially in important features such as payments. Good tests also check realistic situations and whether results match what was expected.