Which description correctly defines statement coverage?

Statement coverage is defined as a measure that evaluates the proportion of executable statements in a program that have been exercised or covered by a set of tests. This type of coverage ensures that every statement in the code has been executed at least once during testing, providing insight into potentially untested parts of the codebase.

By focusing specifically on executable statements, statement coverage helps identify areas in the code where testing might be inadequate. This allows testers to understand which parts of the code might contain unnoticed defects. While it can provide valuable insights, it's important to acknowledge that it does not account for the logical paths or the conditions under which statements are executed, which is where other coverage types, like branch coverage, come into play.

The other options do not accurately capture the essence of statement coverage. For instance, simply measuring the number of lines of source code exercised or expressing coverage as a percentage can lead to ambiguity and does not clarify the focus on executable statements specifically. Therefore, identifying statement coverage as a measure of the proportion of executable statements exercised is the most precise and appropriate description.