A way to bid where you set how much on average you’re willing to pay every thousand times your ad is shown (this amount is your target CPM). We’ll optimize bids using your target CPM (tCPM) to help you gain as much unique reach as possible. Some impressions may cost more or less than your tCPM, but altogether Google Ads will try to keep your campaign's average CPM equal to or lower than the tCPM you set.
Target cost-per-thousand impressions is available for video campaigns in Google Ads. For video ad sequence campaigns, tCPM optimizes for sequence completions (meaning, it optimizes for maximizing the number of users that see the entire sequence) instead of unique reach.