| HO or H.O. | |
| —abbreviation for | |
| 1. | head office |
| 2. | (Brit) government Home Office |
| H.O. or H.O. | |
| —abbreviation for | |
| an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle. |
| an extraordinary or unusual thing, person, or event; an exceptional example or instance. |