What a "Tag" is: When you do a Google query for "Tag" this is the first result:
A label attached to someone or something for identification or other information.

This certainly is the root of what a tag is - if we change this to fit more specifically what we are dealing with here a metadata tag is. WikiPedia provides a good definition: [metadata tag's] describe an item and allows it to be found again by browsing or searching. To "Edit a tag" is to "Change the label of the item that is out of place so that it can be found again by browsing or searching"

There are three different ways that you can edit tag information.
  1. Through Rocket Player
  2. Through your media library (iTunes)
  3. Using another 3rd Party tagging application

This tutorial will show you how to edit a tag in Rocket Player. You can find a tutorial on how to edit a tag using iTunes with this link to ehow.
Note: if used with iSyncr, tag edits made in Rocket Player will not be imported into iTunes.
iTunes to Android sync
1. To access this menu, simply long press on an item that needs to be edited.
iTunes to Android sync

2. Here is the "Tag editing" menu - we can change the following items: Title, Artist, Album, Genre, Disc Number, Track Number, Year.
iTunes to Android sync

3. To change an attribute, simply click on the attribute to edit.
iTunes to Android sync

4. We can see that the Artist name is being edited