What do 风、雅、颂 refer to in 《诗经》 《诗经》共有风、雅、颂三个部分，

Are they just chapter titles? Do they have more significance?
風 is general mood (風氣), or social custom (風俗).

in ancient times, there're regional differences between vassal states (諸侯國); after confucius's editing, fifteen "lessons from the state" (國風) were preserved. each groups of poems from the vassal state, shown that particular state's social custom.

雅 is odes of the kingdom (周朝), where the ruler were.

頌 is odes for the purpose of praising in the ancestral temple (宗廟).

the contents, styles of these three groups of poems / odes are significantly different.