CPC
Cost Per Click
What you actually paid per click — not what you bid.
Your bid is the maximum you are willing to pay. Your CPC is what you actually paid, which is usually less. Bidding $2.00 and paying $0.60 is normal.
This distinction matters more than almost anything else in bidding. Your performance data reflects CPCs, not bids. Calculating a new bid from your current bid rather than your realized CPC compounds errors — if someone dropped all bids to $0.05 yesterday, last month's ACOS still reflects the old, higher CPCs, and cutting again from that data would collapse the account.
AutoPPC always calculates from realized CPC.