Harmonization
In music, harmonization is the chordal accompaniment to a line or melody: "Using chords and melodies together, making harmony by stacking scale tones as triads".
A harmonized scale can be created by using each note of a musical scale as a root note for a chord and then by taking other tones within the scale building the rest of a chord.
For example, using an Ionian (major scale)
the root note would become the I major chord,
the second note the ii minor chord,
the third note the iii minor chord,
the fourth note the IV major chord,
the fifth note the V major chord (or even a dominant 7th),
the sixth note the vi minor chord,
the seventh note the vii diminished chord and
the octave would be a I major chord.
Using the minor (aeolian mode) one would have:
i minor,
ii diminished,
(♭)III major,
iv minor,
v minor,
(♭)VI major,
(♭)VII major and
the i minor an octave higher.
Reharmonization
Reharmonization is the technique of taking an existing melodic line and altering the harmony which accompanies it. Typically, a melody is reharmonized to provide musical interest or variety. Another common use of reharmonization is to introduce a new section in the music, such as a coda or bridge.