YY

JJ is an abbreviation for:

Jiu Jitsu , a Japanese martial art
Ju-Jutsu , a German martial art
Jesu Juva , a Latin phrase
Jeff Jarrett , an American professional wrestler
JJ (band) , a Swedish band
JJ (magazine) , a Japanese magazine
JJ1 , a brown bear who immigrated to Germany in 2006
Jason Jr. , the Woods Hole Oceanographic Institution's unmanned diving robot
a manufacturer of cathode ray tubes, State Combine for Electromechanical Products in the Czechoslovak Republic, see Tesla as
for the Texas Hold'em poker starting hand Bube Bube (English Jack Jack, also "Jay Jay")
the Brazilian airline TAM Linhas Aéreas under the IATA airport code
the German band Jupiter Jones

YY as a distinguishing mark on license plates: