Alpha/Beta Quadrant Overview
Omega Leonis was a location 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. (TNG: "Loud As A Whisper"; DIS: "Magic to Make the Sanest Man Go Mad")
In 2257, during the first Federation-Klingon War, this location was occupied by the Klingons. (DIS: "The War Without, The War Within")
In 2259, Omega Leonis' location was labeled on a stellar cartography chart that was seen on the USS Enterprise's ready room viewscreen. This location's symbol was a red Klingon Empire logo, indicating its affiliation with the empire. (SNW: "Strange New Worlds", "Spock Amok")
In the alternate reality of 2259, the Omega Leonis sector block was named after this location. (Star Trek Into Darkness)
This location was only mentioned in writing.
According to Star Trek: Star Charts (p. 61, "United Federation of Planets I") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Omega Leonis was a multi-star with a pair of F-class stars.