eCPM, or effective cost per mille, is a metric used in digital advertising to measure the average revenue generated for every thousand ad impressions. It takes into account both the cost of serving the ad and the revenue earned from it, providing a more accurate representation of the ad’s performance. This allows advertisers to compare the effectiveness of different ad campaigns and make informed decisions on where to allocate their budget. eCPM is a crucial tool in the world of online advertising, helping businesses maximize their return on investment and reach their target audience more efficiently.