Frequency
Average number of times each user has seen your ad.
Frequency = impressions ÷ reach. It tells you how often the same person is being shown the same ad. Once frequency passes ~3.0 on Meta, performance typically declines — users are saturated and CTR drops while CPM stays the same.
Watch frequency at the ad-set level, not the account level. A retargeting ad set may run at frequency 8 and still convert (intent is high), while a prospecting ad set at frequency 4 needs new creative urgently. Refresh creative every 7–14 days for high-spend campaigns; every 21–30 for slower-spend.