An idiom is a collection of words which means more than the sum of the meanings of each of the phrases' individual words. Verse Dt16-09a discussing the requirements to count 7 weeks from Passover to Shavuoth states Seven weeks shalt thou number unto thee; from the time the sickle is on the sheaf [harvest] shalt thou begin to number seven weeks. . Rashi explains: The phrase(s) the sickle is on the sheaf is an idiom meaning harvest. As can be seen from the underlined words the Rashi comment is compactly and explicitly combined in the Biblical text.

Advanced Rashi: Rashi goes a step further and states The omer coincides with the beginning of the harvest. Rashi learns this from the explicit association in Lv23-10:11. In fact we could have approached this whole Rashi using an alignment of the Lv and Dt chapters both of which deal with the Passover-Omer-Shavuoth sequence. However, it was also important to emphasize that Rashi was identifying a Biblical idiom which is why we classified this Rashi as we did.