An organism that does not need free-form oxygen for growth. Many anaerobes are even
sensitive to free oxygen. Obligate (strict) anaerobes grow only in the absence of
oxygen. Facultative anaerobes can grow either in the presence or in the absence of
molecular oxygen.
Source:
PAC, 1992, 64, 143
(Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992))
on page 146