What does Consonant and dissonant mean in music?

Answer 1

There are 3 times where this terminology will come into play.

the first is in relation to a single note in the chord. a "dissonant" note is normally a 1/2 step or a tritone (augmented 4th) away from a chord tone, creating an unstable or tense sounding interval or chord. for instance if you play an Ab over a C major Chord, you will notice dissonance because Ab is one 1/2step from G (the fifth of the chord).Note that this terminology can only relate a note to a chord. that is a note cannot be dissonant in relation to nothing, it's classification is dependent on the chord it is surrounded by. a consonant note merely belongs in the chord, it is a chord tone or other note in the key signature that does not result in tension. C E G are all consonant notes in a C Chord (but they are all dissonant in an F# chord)

The second is in relation to a chord itself. if a chord has one or more dissonant notes it sounds tense/unstable and can be called a dissonant chord, where a consonant chord sounds stable.

The third is in relation to an entire piece or phrase. this is entirely arbitrary as a piece can have dozens of dissonant chords, but progress and resolve in such a way for it to sound stable. or vice versa, a piece may have many consonant chords but not resolve, or end on a dissonant chord to give an overall dissonant impression.