A cubic parsec (parsec3) was a volume of space equivalent to a cube measuring one parsec on each side. Likewise, a cubic light year (ly3) was a volume of space equivalent to a cube measuring one light year on each side.
After Thomas Riker hijacked the USS Defiant, he later hid in Cardassian space, the unsuccessful search for the cloaked ship included twenty-six Cardassian warships scaning 14 cubic light years of space with anti-proton beams. (DS9: "Defiant")
When Captain James T. Kirk was abducted from the USS Enterprise after entering Metron space while pursuing a Gorn starship in 2266, the only thing Spock was that Kirk was lost "out there somewhere in a 1,000 cubic parsecs of space, and there's absolutely nothing we can do to help him." (TOS: "Arena")