| 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) |