Issue channels are channels that have been created when a user is viewing a JIRA issue and chooses Add Channel in the right panel under Mattermost settings.

See Creating a Mattermost channel from an issue in JIRA.

Here in the Mattermost administration it will list all such channels that have been created via a JIRA issue.  The name of the channel is the key of the JIRA issue. 

To disable an Issue Channel click the

To delete an Issue Channel click .