What ad setting limits the number of times that ad can be shown to a particular user?
- Frequency cap
- Hard cut-off
- Impression ratio
Set a frequency cap to prevent users from seeing an ad too often within a given time period. A frequency cap is the maximum number of times your ad can serve to any given user during the period you set in the Time period field.
Read more here: https://support.google.com/dcm/answer/2837363