CRM lists - Sync Opt-in field

CRM lists - Sync Opt-in field

Hello,  your help files, don't explain what this option is.

"Import only Opt-In contacts - Only Opt-In contacts in Zoho CRM will sync to Zoho Campaings"

Its not obvious either, as there is no field in the CRM that is Opt-in, Only-Opt out, in which it could be an "unchecked" value, means yes, Opt-in. OR does a user actually need to Opt-in from a ZOHO campaign form, before this value is true in ANother field location i the CRM?

Thanks