A microfusion generator was a form of propulsion technology.
Microfusion generators were essential in the lives of the Enarans during the 24th century, on par with a communications interlink. Jareth once noted to his daughter Korenna how hard it was to relate to the Regressives, a group on Enara Prime who used little more than the most primitive technology, including such luxuries as microfusion generators or communications interlinks. (VOY: "Remember")
In the Federation, microfusion generators were found aboard Defiant-class starships. While initiating the impulse pre-start sequence, it was necessary for the microfusion generators to be on line. (DS9: "The Changing Face of Evil")