Parallel keys are a major scale and a minor scale that have the same tonic.
For example, C Major key and C minor key are parallel keys because they have the same tonic note: C
Relationship between parallel keys
There is a relationship between parallel keys:
There is always 3 accidentals less or more, like this:
Minor parallel key + 3# ==> Major parallel key
Major parallel key - 3b ==> Minor parallel
List of most common parallel keys
A flat Major key and A flat minor key
C Major key and C minor key
E Major key and E minor key
F Major key and F minor key
G Major key and G minor key
B Major key and B minor key
B flat Major key and B flat minor key
F sharp Major key and F sharp minor key
D Major key and D minor key
E flat Major key and E flat minor key
C sharp Major key and C sharp minor key
A Major key and A minor key