The Borealis is a crashed Kowloon Class modular freighter on Feros. It was apparently chartered by the salarian merchant Ledra, who promised the crew they could make their fortune on Feros by selling to the colonists of Zhu's Hope much-needed supplies.
Somehow, the Borealis was wrecked on the planet's surface, possibly as a result of the geth attacks, and the colonists began using the Borealis as an impromptu shelter, with the Borealis providing much-needed cover during the various geth raids on Zhu's Hope. Hana Murakami is the last surviving crew member; she mentions that the captain died in one of the geth attacks.
When Commander Shepard arrives on Feros, the colonists have focused their defenses around the Borealis. Hana is apparently running diagnostics on the vessel, claiming the Borealis could still be repaired if she had enough time to do it.
Shepard eventually learns the reason the Borealis is so well-defended; one of the ship's modules is blocking the entrance to the Thorian's lair, to protect it from the geth. When the Commander returns from ExoGeni Corporation's headquarters, the colonists turn on Shepard's team, and defend the ship with their lives.