Noun
1. A condition in which there is oxygen deficiency in a habitat or a body part. (biology-online.org)
2. May refer to:
Hypoxia (environmental), reduced dissolved oxygen content of a body of water detrimental to aerobic organisms.
Hypoxia (medical), a pathological condition in which the body as a whole or region of the body is deprived of adequate oxygen supply.
(wikipedia.org)
3. A reduced concentration of dissolved oxygen in an aquatic environment. (wiktionary.org)
adj., hypoxic