Complex sentence: According to the broadest definition any chord with a nondiatonic note is an altered chord, while the simplest use of altered chords is the use of "borrowed" chords--borrowed from the parallel key.
Split into simpler sentences: According to the broadest definition any chord with a nondiatonic note is an altered chord. The simplest use of altered chords is the use of "borrowed" chords--borrowed from the parallel key.