- An animal (for instance, a mouse raised for experimental purposes) which has no microorganisms whatsoever living in or on it.
- An animal which was born and raised in an isolated environment with no microorganisms in it.
- A chamber which has absolutely no microorganisms whatsoever living in it, where a germ-free animal can be born and raised.
- An artificial barrier surrounding a living facility for germ-free animals, which keeps out all microorganisms.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.