API key
An API key is a long secret password that proves to a service that a request comes from you.
In a simple example
You paste your key into a private settings file, and your app uses it to ask the AI service for answers.
Why it matters to you
Whoever has your key can use your account and spend your money, so keeping it private is your job.
Do not confuse with
An API key is not the same as the login password of your account. It is made for programs, and you can cancel it separately.