The Sigma Erandi system was a planetary star system. This system was located in the Alpha Quadrant.
When the USS Enterprise-D purchased hytritium needed on Beta Agni II from Kivas Fajo in 2366, Fajo told the crew that the next closest source of hytritium was Sigma Erandi, but he could not guarantee they had any on hand. The system was also three weeks away from the Enterprise's current position, so the USS Grissom, the Starfleet vessel closest to Sigma Erandi, was informed to stand by in case more hytritium was needed. (TNG: "The Most Toys")
The Sigma Erandi system appeared in the starchart Data and Picard were studying in Stellar Cartography in 2371. (Star Trek Generations, display graphic)
The star chart seen in "Generations" depicted the location of planets, stars, and star systems in the Alpha Quadrant. Based on the dimensions of the circles used to mark locations on the star chart seen in "Generations", this system was located relatively far to the USS Enterprise-D.