What is the Dual table in Oracle?

Oracle databases contain a table with just one row, this is called 'Dual' table. It may be used in scenarios where in a pseudocolumn like 'User' or 'Sysdate' is being queried.
It has a column called 'Dummy' with data type of varchar2(1) ... 1 being the size.

When this table is queried, it returns a column called 'Dummy'
with a value 'X'

select * from dual;

select sysdate from dual;