All versions of Oracle database. Add a version-specific tag like oracle-11g-r2 if that context is important in the question. Do not use for Oracle products such as applications or middleware or other database products owned by Oracle, like MySQL or BerkeleyDB.
Oracle is a relational DBMS (Database Management System) created by Oracle Corporation. It supports a large number of languages and application development frameworks. Its primary languages are SQL, PL/SQL and Java. When asking a question with the oracle tag, please be sure to include the full version number, (i.e., 10.2.0.5, 184.108.40.206), in addition the relevant version-related tags described below.
Oracle makes plethora of documentation available at http://docs.oracle.com.
Questions applicable to other versions should be tagged as noted above.