Conversions: A conversion is a goal you've set for your campaigns, like a sale or a sign-up. You can track conversions to see how well your campaign is performing. Once conversions have been tracked, you will be able to use metrics like ‘Conversions’ and ‘Conversion Rate’ in your account.
Conversion (site) : when a user performs some specified action after clicking an ad or viewing a Display Network ad, such as purchasing a product, installing a mobile app, or signing up for an email list.
When creating your goal, it is important to establish what sites, or tools are needed to track the conversions.
Examples are : Sign up forms, emails (directly to you), phone calls, downloading a freebie, selling a course or item on your website, booking a consultation, etc.
Please note : ALL conversion sites have to have the URL that matches your domain. This is important when adding to an email list or booking a consultation, since these are typically directed to their sites.