Zero gravity (also called zero-g or null gravity) is the natural feeling of weightlessness experienced by space travellers on extra-vehicular activity or dwellers in spacecraft or space stations where living space lacks artificial gravity.
History and specifics
By 2150, Earth starships possessed artificial gravity technology, but ship arrangement sometimes led to field differentials resulting in small areas of zero gravity. Travis Mayweather referred to these areas as "sweet spots." (ENT episode: "Broken Bow")