Computed columns are (by default) virtual columns not physically stored in the table. : Computed Columns « Table « SQL Server / T-SQL Tutorial

1. SQL Server / T-SQL Tutorial
2. Table
3. Computed Columns

Their values are recalculated each time they are referenced in a query.

CREATE TABLE orders
        (orderid INT NOT NULL,
        price MONEY NOT NULL,
        quantity INT NOT NULL,
        orderdate DATETIME NOT NULL,
        total AS price * quantity PERSISTED,
        shippeddate AS DATEADD (DAY, 7, orderdate))
GO

drop table orders;
GO