The IKS Qu' was the version of the USS Enterprise-E which existed in an alternate reality. It had previously been the United Earth Space Probe Agency vessel Enterprise and was one of the final Federation ships to be captured by the Klingon Empire.
In this reality, Jean-Luc Picard was a slave and all of his crew were executed by the Klingons who began to use his ship as their own. William T. Riker's throat was cut, Data was disassembled, Geordi La Forge was disemboweled, Tasha Yar was shot while attempting escape, Deanna Troi and Beverly Crusher were violated and then strangled. Michael Argyle was decapitated. In 2380, General Mogh was in command. When the Qu' was sent to the primary universe, it opened fire on the Enterprise indigenous to that reality.
Qu' is the Klingon word for "enterprise."