Alias in SQL

[Ankit Dixit]

Hello All, I am working on SQL project and I want to the syntax 
of Alias in SQL? and what is the use of an alias in sql? I have 
checked the source 
https://www.interviewbit.com/sql-interview-questions/ that 
provides the syntax which I mention below. Can anyone explain me?

SELECT A.emp_name AS "Employee" /* Alias using AS keyword */
B.emp_name AS "Supervisor"
FROM employee A, employee B /* Alias without AS keyword */
WHERE A.emp_sup = B.emp_id;