Software Security Fundamentals are the shared language and disciplined approach that modern teams rely on to build safer software from the start, ensuring security becomes a natural part of everyday development rather than an afterthought, shaping architectural choices, cross-functional collaboration rituals, risk assessments, and release planning across engineering, security, and product domains, and embedding security considerations into estimations, roadmaps, and customer expectations.By embracing secure coding practices, developers validate inputs, handle errors securely, resist injection attacks, leverage safe libraries, apply language-specific guidance, and participate in peer reviews to codify safety into day-to-day work, which reduces vulnerabilities at the source and supports reliable behavior across platforms, teams, and deployment contexts, and it also emphasizes safe defaults, structured peer reviews, and the use of feature flags to enable controlled experimentation without compromising security.