I read about "rollbacks", and found questions about "editing rollbacks', but I don't know what it means. Could anybody explain it?
When edits are made to a post (i.e. a question or answer), the revision history for the post has the option to revert the post to a previous revision. Doing so is called doing a 'rollback', since you're 'rolling back' the state of the post to a previous one.
To get to a revision history of a post, find a post that's been edited. You'll see something like this at the end of the post, click the link:
You'll then be on the revision history for the post. If you scroll to a previous revision, you'll see this:
Do not click the link unless you actually need to rollback a post!
Usually, you'll rollback a post if there was vandalism, or the edits didn't improve the post in a substantial way.
I just noticed the question was tagged tags, so I should address tag wikis, just in case. A lot of the above still applies in general, but the mechanism is slightly different. To access a tag wiki's revision history, first click the tag. You'll be presented with a list of questions that have that tag. Click the 'info' tab to get to the full tag wiki. Underneath it, click 'history' to see the revision history, or click 'excerpt history' to see the tag wiki excerpt's revision history.