Line coverage is a metric used in software testing to determine the percentage of executable lines of code that have been tested. It helps identify which parts of the code have been exercised by test cases and which have not. By ensuring that more lines are covered, developers can increase the likelihood of finding bugs and improving code quality. This metric is part of a broader category known as code coverage, which also includes other measures like branch coverage and function coverage. Tools that analyze line coverage can provide insights into untested areas, guiding developers to create more effective test cases and enhance overall software reliability.