Promolinks can be conceptually assimilated to google adwords: independently from the indexed content, it allows the search expert to display text in a dedicated place on the screen (usually on top or on the side). This display is triggered by the presence of specific terms in the search query.
For instance, the illustration below shows a promolink entitled "Nice title" which has the content “report” and is displayed because the keyword "report" was used in the search query:
