pseudocolumns are the columns which are created by itself 
when the table is created. The examples of the 
pseudocolumns are rownum, rowid, currval, nextval and the 
level

psedocolumns are the columns which can not be manipulated.
psedocoluns are only retrive. Examples are rowid,nextval etc

A pseudocolumn behaves like a table column, but is not 
actually stored in the table. You can select from 
pseudocolumns, but you cannot insert, update, or delete 
their values.

Pseudocolumns are not actual columns in a table but they 
behave like columns. For example, you can select values 
from a pseudocolumn. However, you cannot insert into, 
update, or delete from a pseudocolumn. Also, pseudocolumns 
are allowed in SQL statements, but not in procedural 
statements. PL/SQL recognizes the following SQL 
pseudocolumns, which return specific data items: CURRVAL, 
LEVEL, NEXTVAL, ROWID, and ROWNUM.