Although there are many more modes in jazz, classically, there is the major and minor. Minor can be further classified into harmonic and melodic, although we’ll be focusing on harmonic.
Major has a particularly happy sound to it, whereas minor sounds a bit sad.
The difference between major and minor depend on the relative positions of the semitones and tones between notes. For the chord, this is particularly for the third, where for the minor, it is pushed down a semitone, as compared with the major.