I have often seen this phrase used in at least two frequent contexts,
One uses the notation of $\omega_{AB}$ (the matrix $\{ [0 , I],[-I,0]\}$) to denote the symplectic form for $USp$ group.
One uses the notation $\epsilon_{AB}$ (the matrix $\{[1,0],[0,-1]\}$) for $SU(2)$
I would like to know what is the precise definition and meaning of this.