The Orb of Time was one of nine orbs of the Prophets sent to the Bajoran people over a 10,000 year period.
During the Cardassian occupation of Bajor the orb was confiscated by the Cardassians and shipped off the planet. In 2373, the orb was returned to the Bajoran people. During transiting the orb back to Bajor the USS Defiant was sent back in time using the orb in an attempt to alter history. The plot was stopped and the orb was used to return the Defiant to the correct time. (DS9: "Trials and Tribble-ations")