AOV
Average Order Value
Average revenue per order. Sets how much a conversion can afford to cost.
AOV × target ACOS gives your target cost per acquisition. A $30 product at a 30% target can afford $9 of ad spend per order. A $200 product at 25% can afford $50.
This is why fixed spend thresholds are wrong. "Pause anything over $20 with no sales" is far too aggressive for the $200 product and far too patient for the $30 one.