Source code comments are annotations that developers insert into code to describe functionality, provide context, or leave notes for future maintenance. While they are not executed by the program, they play a significant role in secure coding. Well-written comments help teams maintain consistency and reduce misunderstandings when modifying code. However, comments must be carefully managed. Sensitive information, such as credentials, keys, or server details, should never be stored in comments, since source code may be shared publicly or accidentally leaked. Properly used comments improve maintainability and reduce the risk of introducing new vulnerabilities when the code is updated.