what is environmental variable(what object used to deploy application to another environment in appian)?

You don't use objects to deploy other objects. Appian has its own infra for managing the deployments. 
find it here - https://docs.appian.com/suite/help/23.1/compare-deployment-packages.html

Also, environmental variables are environment-specific constants whos value changes when you deploy it. Eg. constant containing your support email address for the current environment.

We have the public Appian documentation. There your will find your question answered.

https://docs.appian.com/suite/help/23.2/Constants.html#overview