The importance of security testing in software development lies in its role in identifying vulnerabilities within an application before it is deployed. By systematically evaluating software for potential threats, developers can mitigate risks associated with data breaches, malware, and unauthorized access. Security testing encompasses various methods, including penetration testing, code reviews, and vulnerability assessments. Prioritizing security not only protects sensitive user information but also builds trust in the product, ultimately contributing to greater overall quality assurance and user satisfaction.