Is a TrackBack an entry?
Trackbacks, comments, entries... All the same thing, varying only by whether or not they are related to another entry and, if so, on where they are hosted (trackbacks hosted by their author, comments hosted by the author of the entry being commented on). See IsaCommentAnEntryDiscussion
Need a TrackBackExample
Is a TrackBack different from a comment?
Let's distinguish between Entry-related-by-Trackback and Trackback protocol.
There are two aspects to a Entry-related-by-Trackback: the data model and the display. The data model is a relation between two Entries (Related) - the remote Entry notifies the local Entry that it is citing. Assuming a Comment is treated as an Entry (IsaCommentAnEntry) then the same kind of relation exists between Entry-related-by-Trackback and Comment. From the perspective of the Entry data model, a Comment and a remote Entry-related-by-Trackback are the same, though they will be distingished by "role".
As for the display of Entry-related-by-Trackback, this is client-dependent. It may be shown as a Comment, shown separately, or not shown at all.