What is the difference between CLOB and NCLOB?

A CLOB stores character data encoded in the database character set. A NCLOB stores character data encoded in the national character set

SELECT parameter, value
  FROM v$nls_parameters
 WHERE parameter LIKE '%CHARACTERSET'

will show you the database and national character sets of your database.

BLOB, CLOB, NCLOB and BFILE The built-in LOB data types BLOB, CLOB and NCLOB (stored internally), and BFILE (stored externally), can store large and unstructured data such as text, images and spatial data up to 4 gigabytes in size.

BLOB

The BLOB data type stores binary large objects. BLOB can store up to 4 gigabytes of binary data.

CLOB

The CBLOB data type stores character large objects. CLOB can store up to 4 gigabytes of character data.

NCLOB

The NCBLOB data type stores character large objects in multibyte national character set. NCLOB can store up to 4 gigabytes of character data.

BFILE

The BFILE data type enables access to binary file LOBs that are stored in file systems outside the Oracle database. A BFILE column stores a locator, which serves as a pointer to a binary file on the server's file system. The maximum file size supported is 4 gigabytes.