Closed outbound change sets and cloning
Key Takeaway
Uploading closes and freezes an outbound change set. To redeploy the same components with their latest changes, clone it, upload the clone, and have the target org deploy it.
An outbound change set packages customizations from the org you are logged into so you can send them to another org. Uploading closes the change set and freezes it. Cloning makes a new, editable copy, so you can fix the change set, add to it, or redeploy the same components.
What an outbound change set is
The org where you create an outbound change set is the source org. The org you send it to is the target org.
You typically build and test customizations in a sandbox and then send them to production. So a sandbox is usually the source org, and production is usually the target org.
Creating, editing, or uploading an outbound change set requires the "Create and Upload Change Sets" permission.