Secure coding is the practice of writing software with security built into the development process. It means thinking about authentication, input validation, error handling, data protection, and access control while code is being designed and reviewed, not after release.
This matters because many attacks exploit ordinary programming mistakes: unchecked user input, weak session logic, insecure deserialization, hard-coded secrets, or memory-safety bugs. When teams use secure coding practices, they reduce the attack surface and make exploitation harder. In defense, this shows up through code review, threat modeling, secure libraries, testing, and developer training. The goal is not to make code perfect, but to catch weaknesses early, before they become costly incidents in production.