What is the difference between User and Schema  in oracle database?

Both user and schema are database user accounts.

When we create a user in oracle database, it is a normal user that has unique user name, authentication method, default tablespace, temporary tablespace, user profile, lock status and so on.

When we create database objects using the authenticated user, the user becomes a schema, owns database objects.

Database objects are tables, views, sequences, constraints, indexes, functions, procedures, packages  and so on.

Therefore, the basic difference between user and schema is that a user does not contain database objects but schema does.