An arva node is a piece of technology used aboard starships piloted by the Tosk in the Hunt. They are similar to Starfleet's ramscoops in that they capture stellar gases and convert them into fuel.
In 2369, the arva nodes of a ship piloted by a Tosk were damaged in a Hunter attack, necessitating their replacement when he docked his ship at Deep Space 9. (DS9 episode: "Captive Pursuit")
In 2376, the humidity mesh over the arva nodes of a Tosk ship was cracked, forcing him to land on Ee to make repairs. (DS9 novel: Rising Son)