OWD (Organization-Wide Defaults) in salesforce is the baseline level of access that the most restricted user should have. Organizational Wide Defaults are used to restrict access. You grant access through other means like(Role Hierarchy, Sharing rules, Sales Teams, and Account teams, Manual sharing, Apex Sharing ).
- Private:- only owner and above hierarchy users can have Read/Write access and below hierarchy, users don't have any access
- Public Read-only:- only owner and above hierarchy users can have Read/Write access and below hierarchy, users can have only Read-Only access
- Public Read/Write:- Irrespective of role hierarchy every one can have Read/Write permissions on the records