>>>In the book I use (SQL 2005 Unleashed) the author is using the following naming convention for UNIQUE constraint:
>>>AK_TABLENAME_FIELDNAME
>>>
>>>Do you think AK stands for Alternative Key? Or what else could it be?
>>>
>>>Also, how important and where do you use the names of constraints (other than when you create them)?
>>
>>If you need to drop a constraint, you need a name.
>
>I understand. But it is not used anywhere in my code, right? That is, if a constrained stops the update does the error message contain the constraint name? (if so, the user will see it and there it is important).

The constraint names are used in table creation scripts.