SQL DEFAULT constraint
A column default is some value or function that the column will take when an INSERT statement doesn't explicitly assign a particular value. In other words, the column default is what the column will get as a value by default.[MSDN]
Example of SQL DEFAULT constraint
The following SQL query creates a DEFAULT constraint on the "Address" column when the "Customers" table is created:
CREATE TABLE Customers
Cust_ID int NOT NULL,
LastName varchar(255) NOT NULL,
Address varchar(255) DEFAULT '123 L.A US'