Compound or Simple?
This bit is easy: 'SIMPLE INTERVALS' are smaller than one Octave, 'COMPOUND INTERVALS' are bigger than one Octave. 'Nuff said.
Melodic and Harmonic Intervals
So's this bit: A 'HARMONIC INTERVAL' has both notes played simultaneously (i.e. together at the same time), a 'MELODIC INTERVAL' has both notes played in succession (i.e. one after the other).
And finally...
Chromatic and Diatonic Semi-tones
A 'CHROMATIC SEMI-TONE' defines the distance between two notes that are a Semi-tone apart but share the same name (e.g. B-Bb), a 'DIATONIC SEMI-TONE' defines the distance between two notes that are a Semi-tone apart and have different names (e.g. F#-G).
