Smart Goals are implicit conversions detected automatically. Google Analytics examine dozens of signals about the website sessions to determine which of those are most likely to result in conversions. Smart Goals are the approximately the top 5% of your website traffic.
The requirements to have Smart Goals are more than 250 clicks over the past 30 days for the selected view. The reporting view must not receive more than 10 million sessions in 30 days or more than 1 million hits per day.
If Advertisers are not using direct conversions (like lead generation or sales) Smart Goals can be used on Adwords to optimize the campaigns, as these Google Analytics sessions are the best users engaging with the website.
How to set up Smart Goals on Google Analytics
On Google Analytics, go to the Admin area. On the View, click on Goals, and there you can create Smart Goal as a goal.
Article source: https://ppc.land/2018/01/24/how-to-use-smart-goals-in-google-analytics/