Tasso in particular, Mirollo notes, treated the concetto "as the equivalent in a lyric poem of plot in longer works." Pellegrino, similarly, and with reference to Tasso, says that concetti "are the soul and the form of a composition" […]
Source: wiktionary
But to restrict the concetto to an idea or concept gives short shrift to the metaphorical and sometimes occult implications of the term. Conceit as discors concordia involves the comparison of unlike things, the finding of similarity in dissimilarity.
Source: wiktionary