| H | Hecto | - | Astronomy |
| H | Henry - Hydrogen | - | Astronomy |
| H.C. | Honoris Causa (Latin | - | Astronomy |
| H/MAD | High/Medium Altitude Air Defence (aytchmad; See Also HIMAD) | - | Astronomy |
| HA | Haiti (FIPS 10-4 Country Code) -High Availability | - | Astronomy |
| HA | Hausa Language (ISO 639-1 Code) - Hectare | - | Astronomy |
| HAART | Highly Active Anti-Retroviral Therapy | - | Astronomy |
| HAI | Human Awareness Institute | - | Astronomy |
| HAL | Hardware Abstraction Layer | - | Astronomy |
| HALO | High Altitude Low Opening (parachute Jump) | - | Astronomy |
| HALT | Hungry Angry Lonely Tired | - | Astronomy |
| HANS | Head And Neck Support (device Used In Many Race Cars) | - | Astronomy |
| HARM | High-speed Anti-Radiation Missile | - | Astronomy |
| HAT | Highest Astronomical Tide (nautical Charts) -Hungarian Automated Telescope | - | Astronomy |
| HAT | Haitian Creole Language (ISO 639-2 Code) | - | Astronomy |
| HAU | Hausa Language (ISO 639-2 Code) | - | Astronomy |
| HAW | Heavy Antitank Weapon | - | Astronomy |
| HAWK | Homing All The Way Killer (air Defence System) | - | Astronomy |
| HAZ | Heat-Affected Zone | - | Astronomy |
| HAZMAT | Hazardous Materials | - | Astronomy |
| HBCD | HexaBromoCycloDodecane | - | Astronomy |
| HBO | Home Box Office | - | Astronomy |
| HBR | Human Behaviour Representation | - | Astronomy |
| HBT | Heterojunction Bipolar Transistor | - | Astronomy |
| HBV | Hepatitis B Virus | - | Astronomy |
| HCCI | Homogeneous Charge Compression Ignition | - | Astronomy |
| HCF | Highest Common Factor | - | Astronomy |
| HCI | Human-Computer Interaction/Interface | - | Astronomy |
| HCSC | Higher Command And Staff Course | - | Astronomy |
| HCT | Higher Colleges Of Technology | - | Astronomy |
| HD | Henry Draper (star Catalogue) - Hull-Down (armoured Vehicle Target | - | Astronomy |
| HDD | Hard Disk Drive - High-Density Disk | - | Astronomy |
| HDL | High-Density Lipoprotein | - | Astronomy |
| HDM | Human Decision-Making | - | Astronomy |
| HDRA | Henry Doubleday Research Association | - | Astronomy |
| HDTV | High-Definition Television | - | Astronomy |
| HE | High Explosive | - | Astronomy |
| HE | Hebrew Language (ISO 639-1 Code) | - | Astronomy |
| HE | Helium | - | Astronomy |
| HEAT | High Explosive Anti-Tank (ammunition) | - | Astronomy |
| HEB | Hebrew Language (ISO 639-2 Code) | - | Astronomy |
| HEER | High-Explosive Extended Range (ammunition) | - | Astronomy |
| HEIC | Honourable East India Company | - | Astronomy |
| HEMP | High-Altitude Electromagnetic Pulse | - | Astronomy |
| HEO | Highly Elliptical Orbit | - | Astronomy |
| HEOSS | High Earth Orbit Space Surveillance | - | Astronomy |
| HEP | High-Explosive Plastic (ammunition) | - | Astronomy |
| HEPA | High-Efficiency Particulate Air (filter) | - | Astronomy |
| HER | Herero Language (ISO 639-2 Code) | - | Astronomy |
| HESH | High-Explosive | - | Astronomy |
| HESV | Heavy Engineering Support Vehicle | - | Astronomy |
| HETT | Heavy Equipment Transporting Truck / Heavy Equipment Truck Tractor | - | Astronomy |
| HEU | Highly Enriched Uranium | - | Astronomy |
| HF | High Frequency | - | Astronomy |
| HF | Hafnium | - | Astronomy |
| HFAC | Human Factors (aytchfak) | - | Astronomy |
| HFE | Human Fertilisation And Embryology (UK Act) | - | Astronomy |
| HFEA | Human Fertilisation And Embryology Authority (UK) | - | Astronomy |
| HG | Mercury (Latin Hydrargyrum) | - | Astronomy |
| HGC | UK Human Genetics Commission | - | Astronomy |
| HGF | Human Growth Factor | - | Astronomy |
| HHD | Humanitatum Doctor (Latin | - | Astronomy |
| HI | Hawaii (postal Symbol) | - | Astronomy |
| HI | Hindi Language (ISO 639-1 Code) | - | Astronomy |
| HIDACZ | High-Density Airspace Control Zone (high Dak Zed/zee) | - | Astronomy |
| HIH | His (or Her) Imperial Highness | - | Astronomy |
| HIM | His (or Her) Imperial Majesty | - | Astronomy |
| HIMAD | High To Medium Altitude Air Defence (see Also H/MAD) | - | Astronomy |
| HIMEZ | High Altitude Missile Engagement Zone | - | Astronomy |
| HIN | Hindi Language (ISO 639-2 Code) | - | Astronomy |
| HIPAA | U.S. Health Insurance Portability And Accountability Act | - | Astronomy |
| HIPPARCOS | HIgh Precision Parallax COllecting Satellite | - | Astronomy |
| HIRD | Hurd Of Interfaces Representing Depth (cf. HURD) | - | Astronomy |
| HIRISE | High Resolution Imaging Science Experiment | - | Astronomy |
| HIT | Head Injection Technology | - | Astronomy |
| HIV | Human Immunodeficiency Virus | - | Astronomy |
| HIWT | Hobart Institute Of Welding Technology | - | Astronomy |
| HJ | Hic Jacet (Latin | - | Astronomy |
| HJD | Heliocentric Julian Day | - | Astronomy |
| HK | Hong Kong (ISO 3166 Digram; FIPS 10-4 Territory Code) | - | Astronomy |
| HKD | Hong Kong Dollar (ISO 4217 Currency Code) | - | Astronomy |
| HKG | Hong Kong (ISO 3166 Trigram) | - | Astronomy |
| HKS | HyperKinetic Syndrome | - | Astronomy |
| HL | Holding Line | - | Astronomy |
| HL | Hectolitre | - | Astronomy |
| HLA | High Level Architecture - Human Leukocyte Antigen | - | Astronomy |
| HLL | High-Level Language | - | Astronomy |
| HLS | Hoc Loco Situs (Latin | - | Astronomy |
| HLVW | Heavy Logistics Vehicle | - | Astronomy |
| HM | Heard Island And McDonald Islands (ISO 3166 Digram; FIPS 10-4 Territory Code) | - | Astronomy |
| HMCE | Her Majesty's Customs And Excise | - | Astronomy |
| HMCS | Her Majesty's Canadian Ship Or Her Majesty's Courts Service | - | Astronomy |
| HMD | Heard And McDonald Islands (ISO 3166 Trigram) | - | Astronomy |
| HMF | HydroxyMethyl Furfural | - | Astronomy |
| HMM | Hidden Markov Model | - | Astronomy |
| HMMWV | High Mobility Multipurpose Wheeled Vehicle (hum-vee; Hummer) | - | Astronomy |
| HMO | Health Management Organization | - | Astronomy |
| HMO | Hiri Motu Language (ISO 639-2 Code) | - | Astronomy |
| HMP | Her Majesty's Prison | - | Astronomy |
| HMS | Helmet-mounted Display - Her Majesty's Ship (Royal Navy) | - | Astronomy |
