HM can signify:

• Air Seychelles: IATA code
• Heard Island and McDonald Islands: ISO 3166 digram and FIPS PUB 10-4 territory code
• Hindley-Milner, a type system.
• HM (patient), pseudonym of a man with no long-term memory (also written H.M.)
• HM Magazine, a Christian Hard rock magazine
• His Majesty/Her Majesty, a form of address for a monarch and his/her consort, often prefixing something that (theoretically) belongs to said monarch such as HM Government, HM Ship, etc.
• H&M, or Hennes & Mauritz, a Swedish clothing company
• Harvest Moon series, farm simulation/role-playing video games produced by Victor Interactive Software (acquired by Marvelous Interactive in 2002)
• Hidden Machine, in the video game series Pokémon.
• Hamburger Mary's, a restaurant chain
• HM is also the abbreviation code for the rating of Hospital Corpsman in the United States Navy.
• The Haunted Mansion
• Fender HM Strat, a superstrat electric guitar.

hm can signify:

• hectometre, an SI unit of length

Hm | Hm | HM | HM | Hm