Perseus Veil

The Perseus Veil is a huge nebula of opaque gas and dust that separates geth space from the Terminus Systems. After the Geth War with the quarians, the geth isolated themselves behind the Veil, far from the eyes of organic races. The Veil is almost impossible to scan through or navigate, meaning no one knows exactly what the geth are doing beyond it.

Exploring near the Perseus Veil is exceptionally dangerous, but some people risk it because there are sometimes rich salvage pickings nearby.

There seems to be Reaper debris near the Perseus Veil. The crew of the MSV Cornucopia discovered a mysterious artifact that destroyed their minds with indoctrination and compelled them to pilot their ship straight into the Veil. The geth turned the crew into Husks and sent them back into normal space as a warning.

The most important discovery near the Perseus Veil was Sovereign, found by Edan Had'dah's survey team and later reactivated or awakened by Saren Arterius. Sovereign's presence near the Perseus Veil is unexplained, but it may have been there to monitor the geth, or the geth themselves chose territory close to their 'god'.

(Source: Galactic Codex: Essentials Edition 2183.)