Alpha/Beta Quadrant Overview
No'Mat, also known as Omicron Leonis, was a star in Klingon space, in the Beta Quadrant.
In 2256, its location was labeled on the star chart "Alpha/Beta Quadrant Overview" in the ready room aboard the USS Discovery. (DIS: "Magic to Make the Sanest Man Go Mad", "The War Without, The War Within")
A year later, its location was labeled on the star chart showing the trajectory of Lieutenant Spock's shuttle. (DIS: "An Obol for Charon")
In 2258, the star's location was labeled on a star chart seen on the main viewscreen of the USS Enterprise. (DIS: "Such Sweet Sorrow, Part 2")
In 2259, the location of this star was labeled on a stellar cartography chart that was seen on the USS Enterprise's ready room viewscreen. This star's symbol was a red Klingon Empire logo, indicating its affiliation with the empire. (SNW: "Strange New Worlds", "Children of the Comet", "Spock Amok")
In 2399, its location was labeled a Federation star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. This star was located in or near to Klingon space. (PIC: "Maps and Legends")
In the late 32nd century, this star was located in the Klingon Zone. (DIS: "There Is A Tide...")
This location was only mentioned in writing.
According to the Star Trek: Star Charts (p. 62) and Stellar Cartography: The Starfleet Reference Library ("Stellar Cartography", pp. 27, 30; "Federation Historical Highlights, 2161-2385"), No'Mat (Omicron Leonis) was a multi-star with a pair of F-class stars and an A-class star. According to a map of the Klingon Empire – prepared by the Scribe K'Tark for the Klingon High Council in the Year of Kahless 893 (2266) – No'Mat was identified as a Klingon system.