An idea is a feat of association, and the height of it is a good metaphor.
Plato asserted that there is a realm of Forms or Ideas which exist apart from the one who may have thought of these ideas. Material things are then transient reflections or instantiations of unchanging ideas. Consequently, Plato considered that knowledge of material things is not really knowledge; real knowledge can only be had of unchanging ideas.
Of Plato I draw no conclusions, but If indeed Idea and ideas or as old as the wind, they seem to move among us not just on the the back of the wind, but also on the soles of the feet, the tip of the tongue, the misplaced thing, and also in dream.