The Alwanir Nebula was an interstellar gas cloud.
In late 2369, the USS Enterprise-D conducted three spectral analyzes of the Alwanir Nebula, each on a different frequency, while en route to the Gariman sector. (TNG: "Rightful Heir")
According to the script, the pronunciation for Alwanir was "al-WAH-ner". [1]
According to the Star Trek: Star Charts, on page 64, the Alawanir Nebula was located in the Beta Quadrant.