Discussions
Discussions are automatically created when you comment on an object. They are the connection between an object and it's comments.
There can be multiple discussions with different channels attached to an object that you can use as needed.
Basic Use
Assuming you have a subject object like a page, post, or otherwise, you can get the default subject like so:
{% set discussion = subject.discussion %}
Optionally you can provide a specific channel you would like to fetch:
{% set privateDiscussion = subject.discussion('private') %}
Using Discussions
Typically you would use your discussion to fetch comments. More on that in the comments section.
{% set comments = subject.discussion('private').comments %}