Each table in a database instance has a unique name.
If you specify a table name in an SQL statement without specifying an owner or a schema, then the database system searches through the database catalog for the table name in the following order:
1. Catalog part of the current owner
2. Set of PUBLIC synonyms
3. Catalog part of the database administrator who created the user currently logged on
4. Catalog part of the database system administrator
5. Catalog part of the owner of the system tables
You can only access tables from another owner or schema if you already have the necessary privileges.
SQL Reference Manual,