means The central idea, recurring subject, or unifying concept that runs through a piece of writing, art, music, conversation, or event.

from From the Greek 'thema,' meaning 'something set down' or 'a proposition,' from the root 'tithenai,' 'to put or place' — literally the thing you lay out for examination. It traveled through Latin 'thema' and Old French before settling into English, carrying its sense of a deliberately stated subject. That same 'place-setting' root is a distant cousin of words like 'thesis.'