HAO
| Acronym | Definition |
|---|---|
| HAO | High Altitude Observatory (US National Center for Atmospheric Research) |
| HAO | High Availability Option |
| HAO | Home Address Option |
| HAO | Hamilton, Ohio (Airport Code) |
| HAO | Hospice Association of Ontario |
| HAO | Humanitarian Affairs Officer |
| HAO | Health Action Overseas |
| HAO | Human Appeal Organization |
| HAO | Humanitarian Assistance Operation |
| HAO | Haute Activité Oxyde (French: High Activity Oxide) |