An environment variable is a in-memory key/value pair that developers use to store configuration details about their app.
Environment variables are excellent places to store sensitive information (such as API keys), or information that needs to be globally accessible from anywhere in the app, (such as version numbers or hardcoded paths).
In addition to letting you define and encrypt environment variables directly in the user interface, App Platform also provides a number of environment variables that you can refer to in your code for things like your database connection details, the hash for your last git commit, and your service’s public routable path.