HARMONY
Harmony is the result of polyphony (more than one note being played simultaneously). Harmony is a study in music theory. The word harmony comes from the Greek ἁρμονία harmonía meaning "a fastening or joint". The concept of harmony dates as far back as Pythagoras. Therefore it is evident why it is used to refer to a connection between people joining in "peace".
An interval is the relationship between pitch two separate musical pitches. For example, in the common tune “Twinkle Twinkle Little Star”, the first two notes (the first “twinkle”) and the second two notes (the second “twinkle”) are at the interval of one fifth. What this means is that if the first two notes were the pitch “C”, the second two notes would be the pitch “G”--four scale notes, or seven chromatic notes (one fifth), above it.