Environment variable
A practical DevOps definition, with an example you can use.
A named value supplied to a process through its execution environment.
An example you can picture
The same application reads PORT in a local container and in a staging environment. The configuration changes without changing the application source.
The distinction that matters
An environment variable is a delivery mechanism, not a secret-management guarantee. Avoid printing credentials or including them in committed configuration.
Put it into practice
Give a harmless setting such as an application port a different value in a local lab. Show that the process reads it, and document how another learner can provide the same setting. Do not use a real credential for this exercise.
Connect the ideas: secret and container. For the bigger picture, read the related learning guide.
Reference
Read the primary documentation for the underlying concept and further detail.