Use the CLOB datatype to store large blocks of single-byte character data "out of line" inside the database. This means that when a table has a CLOB column, a row of data for that table contains a pointer or locator to the actual location of the CLOB data (so it is not "in line" with the other column values of the row).
A CLOB variable contains a locator, which then points to the large block of single-byte character data. CLOBs can be up to 4 gigabytes in size, and they participate fully in transactions. In other words, any changes you make to a CLOB (via the DBMS_LOB built-in package) can be rolled back or committed along with other outstanding changes in your transaction. CLOB locators cannot, however, span transactions or sessions.
Note: Variable-width character sets are not supported in CLOBs.