Oracle Database Instance
https://docs.oracle.com/cd/E11882_01/server.112/e40540/startup.htmOracle System Identifier (SID) The system identifier (SID) is a unique name for an Oracle database instance on a specific host. On UNIX and Linux, Oracle Database uses the SID and Oracle home values to create a key to shared memory. Also, the SID is used by default to locate the parameter file, which is used to locate relevant files such as the database control files.
Oracle Database Instance
docs.oracle.com › cd › E11882_01A database is a set of physical files on disk created by the CREATE DATABASE statement. The instance manages its associated data and serves the users of the database. Every running Oracle database is associated with at least one Oracle database instance. Because an instance exists in memory and a database exists on disk, an instance can exist ...