A credit applied to your account if we've shown your ad so much that you exceed your monthly charging limit. Google doesn't charge you for these clicks and can automatically issue a credit on your invoice.

How it works:

• Overdelivery is when Google Ads shows your ad more than what your budget would normally allow. And this can help make up for those days when your ad doesn't show very much.
• When overdelivery happens, your total daily cost could be up to 2 times your average daily budget. But in a complete monthly billing period, you'll never be charged more than your monthly charging limit -- the average number of days in a month (30.4) multiplied by your average daily budget.
• If Google overdelivers your ads too often, and you accrue more costs in a complete monthly billing period than your budget allows, an overdelivery credit is automatically applied to your account.

More about overdelivery
More about monthly charging limits
More about managing your budget

* Nguồn: Google