Gm7 is a G minor triad with a minor 7th (F note).  This chord is compatible with the  G Dorian ,  G Aeolian , and  G Phrygian  modes.

Gmaj7 is a G major triad with a major 7th (F-sharp note).  This chord is compatible with the  G Lydian  and  G Ionian  modes.