SQL Aliases are defined for columns and tables. Basically aliases is created to make the column selected more readable.
For Example: To select the first name of all the students, the query would be like:
Aliases for columns:
SELECT first_name AS Name FROM student_details;
SELECT first_name Name FROM student_details;
In the above query, the column first_name is given a alias as 'name'. So when the result is displayed the column name appears as 'Name' instead of 'first_name'.