A spaceship propulsion technology the idea of which is to use electromagnetic fields to collect hydrogen from space and fuel a fusion process.

Examples:
The Enterprise-D crew discharged vast amounts of hydrogen from the ship's Bussard collectors in a last ditched attempt to escape from a Tykan's Rift in tng4x17 "Night Terrors".

References:
https://en.wikipedia.org/wiki/Bussard_ramjet