Conversation so far:
What types of melodies did Francis Poulenc create?
Poulenc's music is "directly or indirectly inspired by the purely melodic associations of the human voice.
Who influenced him?
CANNOTANSWER.
What was his style of music like?
Poulenc's music is essentially diatonic.

Question: What do you mean by diatonic?
Self-contained rewrite: What do you mean by diatonic?