(US) Initialism of Health and Human Services.

Initialism of harness hang syndrome.

His Holiness. / His or Her Highness. / Initialism of Hansestadt Hamburg. The German city of Hamburg. (Used on licence plates and informally in other contexts.)

(philately) Initialism of heavily hinged.

Initialism of Heil Hitler.

Abbreviation of hands (one hand being four inches).

The gene coding for the Hh (Hedgehog) protein. / The signaling pathway involving the Hh (Hedgehog) protein, and its homologues in other animals.

(medicine) A blood group system involving the presence of either the H or the h antigen on the surface of a person's red blood cells.

(emergency medicine) Initialism of hyperosmolar hyperglycemic nonketoic coma.

(Internet slang) Initialism of ha ha only serious.