A tag is a keyword that a user adds to an object.
A comment is a linguistic statement or set of statements added to an object or tag by a tagger during an act of tagging.
Source is the place where the object is hosted. It can be Delicious, Flickr, YouTube, etc.
Tagging can be viewed as voting. The value of vote can be represented as the number of different taggers tagging a bookmark, the number of users indicating a resource is a favorite, or the number of users viewing a video.
Date is the time stamp of the tagging behavior. Format is "MmmYY"
Tagging is the concept which is created to link other concepts. Itself does not have any real meaning
Object is the thing which tagger is tagging. It can be bookmarks, photos, videos, musics, books, slides, etc.