The Bitrose sector, situated within the Outer Rim Territories, was a sector that housed the space station known as Roost. This was true, at least until Roost's destruction occurred in 9 ABY.
The initial appearance of the Bitrose sector in canon occurred within the sixth episode of The Mandalorian, titled "Chapter 6: The Prisoner." However, its identification as the Bitrose sector was first established within the reference work, Star Wars Encyclopedia: The Comprehensive Guide to the Star Wars Galaxy.
Regarding Star Wars Legends, the first reference to it can be found in Wanted by Cracken (sourcebook), a supplementary paperback for Star Wars: The Roleplaying Game that was released by West End Games.