A secret API key is a private credential used by software to authenticate to a service and perform actions on its behalf. Unlike a public identifier, it should never be embedded in client-side code, shared in logs, or exposed in screenshots, because anyone who has it may be able to call the API as if they were the legitimate user or application.
In cyber security, leaked API keys are a common source of fraud, data access, and service abuse. Attackers look for keys in source code, build artifacts, chat logs, and misconfigured repositories, then use them to query data, create resources, or rack up costs. Defenders reduce this risk by storing keys in secrets managers, limiting permissions, rotating credentials quickly, and monitoring for unusual API activity. When a key is exposed, treat it like a password: revoke it, replace it, and check what was accessed before the exposure was detected.