The Kalandra sector was a region of Federation space near the core Federation worlds. The Kalandra system was located within it.
In 2374, Dominion forces launched a successful invasion of Betazed from the Kalandra sector, which Starfleet Intelligence had believed too far from their supply lines to be a threat. (DS9: "In the Pale Moonlight") The sector subsequently fell to the Dominion, allowing them to threaten Vulcan. (DS9: "The Reckoning")
Based on Cardassian military transmissions decoded by Elim Garak, Starfleet launched a counter-offensive and retook the Kalandra sector in early 2375. (DS9: "Afterimage")
The sector later served as the rendezvous point after General Martok's raid on Trelka V, where the USS Defiant and seven other Federation starships stood in wait for the returning Klingon forces. (DS9: "Once More Unto the Breach")
The script of "In the Pale Moonlight" spelled the name of this sector as "Calandra" 
According to the Star Trek: Star Charts (p. 49), the Dominion occupied the Kalandra sector in December 2374. In April 2375, the Seventh Fleet launched an offensive into the sector.