Qus: What is OWD?
There are four levels of access that can be set:
By default after creating custom object OWD access level is Public Read/Write.
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.
Public Read/Write: Irrespective of role hierarchy everyone can have Read/Write permissions on the records.