What is the difference between spots and impressions?

A spot is a single ad placement — one radio ad airing, one TV commercial slot, etc. Impressions are the estimated number of people who see or hear an ad. Radio and TV are typically bought by spots (cost per spot), while digital and streaming media are typically bought by impressions (CPM — cost per thousand impressions). The AI planner handles both pricing models and converts between them when building your media mix.