The Gnosis was a Zion hovercraft.
When the Zion ship captains meet within the Matrix for the Crisis Meeting, Gnosis crew members Corrupt and Wurm are assigned to guard the door to the meeting place. When Smith arrives "looking for Neo", Corrupt speaks with him. Both Corrupt and Wurm warn the captains of the arrival of "the Feds", a trio of Matrix Agents.
When the Nebuchadnezzar returns to Zion, Neo is worshiped by some residents who believe he has the power to save them (he is clearly not comfortable with this). One elderly woman asks him to watch over her son, Jacob, who serves aboard the Gnosis.
The Gnosis is part of the fleet sent to intercept the invading Sentinels. The ship is disabled when Bane sets off the EMP and subsequently destroyed.
The name of the Gnosis derives from the Greek word "gnosis", meaning knowledge. Its crew, except Jacob, all have names relating to computing (data can become "corrupt," a "worm" is a type of technological attack, and "ICE," in many cyberpunk works, stands for "Intrusion Countermeasures Electronics," what we would now recognize as anti-virus programs.)