A schema is a collection of database objects owned by a specific database user,or schema objects.Schema has the same name as that user,every user has a single schema,so the two terms(Schema,User) are synonymous.

Schema objects include the segments(tables,indexes..etc) as we can see in the tablespaces as well as the nosegments database objects(constraints,views,procedures,synonyms and packages).But the roles,tablespaces,profiles and directories are not schema objects,cause they are not owned by one specific user.

In a word,if any object(table,view,index…) owned by one user,it’s schema object.Contrarily,the role,profile,tablespace and directory (not owned by one user) are not schema objects.

Note:

There is no relationship between schemas and tablespaces: a tablespace can contain objects from different schemas,and the objects for a schema can be contained in different tablespaces.