HJ may refer to:

Science, technology, and mathematics

Hall–Janko group In the area of modern algebra known as group theory, the Janko group ''J2'' or the Hall-Janko group ''HJ'' is a sporadic simple group of order : 2733527 = 604800 : ≈ 6. History and properties ''J2'' is one of the 26 Spora ...

, a mathematical group * U.S. code for a cryptographic key change; see

cryptoperiod A cryptoperiod is the time span during which a specific key (cryptography), cryptographic key is authorized for use. Common government guidelines range from 1 to 3 years for asymmetric cryptography, and 1 day to 7 days for symmetric cipher traffic ...

Other uses

* , a two-letter combination used in some languages ** /hj/, a pronunciation cluster, sometimes reduced * Holden HJ, an Australian car 1974-1976 * Hajji (Hj.), an Islamic honorific * ''hic jacet'' ('here lies'),

Latin phrase __NOTOC__ This is a list of Wikipedia articles of Latin phrases and their translation into English. ''To view all phrases on a single, lengthy document, see: List of Latin phrases (full)'' The list also is divided alphabetically into twenty page ...

on gravestones *

Hilal-i-Jurat The Hilal-e-Jurat ( ur, , as if it were ''Halāl-e-Jurāt''; English: Crescent of Courage , sometimes spelled as Hilal-e-Jur'at, Hilal-e-Jurat, Hilal-i-Jurrat and Hilal-i-Juraat)Various official sources that are highly reputable spell the name ...

, post-nominal for Pakistan honour * Hitler-Jugend (Hitler Youth) * Tasman Cargo Airlines, IATA airline designator * Handjob {{disambiguation