It's often used to describe:
* Books: An unabridged book contains the entire original text, unlike an abridged version which might have parts cut out.
* Dictionaries: An unabridged dictionary includes all known words and their definitions, while an abridged dictionary might only include a core set of words.
* Recordings: An unabridged recording contains the entire original recording, without any cuts or edits.
The opposite of "unabridged" is abridged, meaning shortened or condensed.