Parallel keys share a tonic but use a different mode (e.g., C major and C minor). You can borrow chords from any parallel mode without leaving the original key center. The borrowed chord adds color while the tonic stays the same.

Most-used borrows in major

• iv — from parallel minor (e.g., Fm in C major, 'Creep')
• bVI — from parallel minor (e.g., Ab in C, anthemic)
• bVII — from Mixolydian / minor (e.g., Bb in C, rock cliché)
• bIII — from parallel minor (e.g., Eb in C, melancholy)
• bII — from Phrygian (e.g., Db in C, 'Neapolitan' chord)