HJ

HJ may refer to:

Science, technology, and mathematics

• Hall–Janko group, a mathematical group
• Hamilton–Jacobi equation, an equation in classical mechanics which also has relations to quantum physics
• U.S. code for a cryptographic key change; see cryptoperiod

Other uses

• ⟨hj⟩, a two-letter combination used in some languages
• hj-reduction in English, dropping the /h/ sound before /j/
• Hajji (Hj.), an Islamic honorific
• Handjob
• hic jacet ('here lies'), Latin phrase on gravestones
• Hilal-i-Jurat, post-nominal for Pakistan honour
• Hitler-Jugend (Hitler Youth)
• Holden HJ, an Australian car 1974-1976
• Hot Jupiter, a type of planet
• Tasman Cargo Airlines, IATA airline designator
• Jiaguwen Heji, the standard comprehensive collection of rubbings of ancient Chinese oracle bone inscriptions
• "High jump" athletics abbreviation in track and field