Although in the audiobook the pronunciation often sounds like “broussard”, the term refers to the molecular trail left behind by the passage of a spacecraft that is using a Bussard ramscoop. The HEAVEN vessels are equipped with a ramscoop generator, which Bob uses to his advantage as he searches for Bender at the beginning of Heaven’s River. He is able to follow the Bussard trail and confirm that Bender had altered course from Gamma Leporis A to Eta Leporis. However, as the trail entered that system it dissipated, due to the gravitational effects of the system and its bodies on the faint trail of molecules.