waste product

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An unusable or unwanted substance or material produced during or as a result of a process, such as metabolism or manufacturing.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun an unwanted material produced during some manufacturing process, especially radioactive material from nuclear reactors
• noun the unwanted results of metabolism, expelled in the urine and faeces

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any materials unused and rejected as worthless or unwanted