A Federation sector fought over during the Dominion War, used by the Dominion as the springboard for its invasion of Betazed and later retaken by Starfleet.
The Kalandra sector is a region of Federation space that changes hands during the Dominion War. It contains the Kalandra system and lies uncomfortably near several core Federation worlds.
In the Deep Space Nine episode In the Pale Moonlight, the Dominion surprises Starfleet by invading Betazed from the sector, which intelligence had judged too far from enemy supply lines to be a threat. The Reckoning notes the danger this advance poses to Vulcan.
In Afterimage, Cardassian transmissions decoded by Garak help Starfleet prepare its effort to win the sector back. By the time of Once More Unto the Breach it serves as the rendezvous where the USS Defiant and other ships wait for Martok's raiders returning from Trelka V.