Which Salesforce org is used to release the app on AppExchange?

We need to be the partner before submitting app in AppExchange. Once you are signed up as a partner, create an AppExchange Publishing Org (APO). In the Partner Portal, you’ll see a big button at the top of the screen labeled, “Create A Test Org.” For org type, select “Partner Developer Org.” You will receive new credentials by email. Be sure to login and set your password before proceeding. Note that the system will pick a username for you. If you don’t like it, feel free to change it. The purpose of this org is to help you publish listings on AppExchange.