vCPM bidding in Google Ads stands for Viewable Cost Per Thousand Impressions. This strategy is similar to tCPM bidding, but it focuses on viewable impressions. Ad impressions are counted as viewable when they meet specific viewability criteria, such as being in the visible portion of the user's screen. This strategy is useful for display campaigns when the goal is to maximise viewable impressions. However, it does not guarantee engagement or conversions.