The significance of using API keys for application security lies in their ability to control access to APIs, ensuring that only authorized users or applications can interact with certain resources. API keys act as a unique identifier for a project or user, granting specific permissions while limiting potential misuse. By implementing API keys, organizations can track usage, monitor access patterns, and prevent unauthorized actions. The secure management of these keys is crucial for maintaining the integrity of applications, protecting sensitive data, and mitigating risks associated with security breaches.