There are times when you write query and end up qualifying the columns references by indicating the table name.
For example ,
SELECT Department.GroupName , Department.Name FROM HumanResources.Department;
In the above query , the Department table is referred in the GroupName and Name column. Instead of mentioning the table table , we could provide a shortname or alias name for the table and use the alias name instead.
SELECT d.GroupName , d.Name FROM HumanResources.Department as d;
The full use of the alias names can be seen especially when you are working joining multiple queries.