The Umani sector was a region of space.
In 2372, the Tavnian Jeyal came to Deep Space 9 aboard a transport from the Umani sector. (DS9: "The Muse")
This sector was only mentioned in dialogue.
Given Lwaxana's reaction upon hearing that someone had arrived from the sector
, it might be the location of Jeyal
According to StarTrek.com
, Umani was either a "namesake star
or other object of the sector".